Well I already discovered that no matter which amp model I use, the higher the master volume, the better the sound gets to me. However someone else mentioned that this is a side effect of playing at low volumes. Thing is, low volumes is what I am stuck with, and don't ever expect to play at higher volume levels. That's one of the main reasons I got the unit. To be able to have good tones at low volume levels, like reasonable TV volume level.
The lower the Master, the more sterile the tone sounds to me.
Anyways a lot of this was an experiment, I was just curious.
As others have already I would suggest taking a different approach to demo'ing each amp. For those amp models whose real-world counterpart have no master volume set it all the way up. For those with a master volume do a search here and on forums where the physical amp is popular, find out what the sweet spot seems to be, and set the master volume similarly. Pick a cabinet IR from the stock list that best matches that used with the real amp - this is especially important for combo amps where the speaker/cab impart much of that particular amps character. For head & cab combinations pick a cab most often used for the amps expected sound (Mesa 4x12 with a Mesa Rec amp, Marshall 4x12 w/ greenbacks with a Marshall JTM45, 4x12 w/ G1265's with a JCM800, Orange 4x12 with an Orange head, etc. Set input gain according to how you would be likely to use the amp and adjust the tone stack (and presence, where applicable) to taste. Find songs where the amp you're working with was used in the recording and try to adjust the input gain and tone stack to cop the basic recorded sound (keeping in mind that many more factors are at play in the recorded track (mic's used, mic placement, many tracks are doubled, effects used). The ides is to try to capture the general character of that particular model as used in a familiar recording. Even if you aren't able to get too close to the target you should have separated the various models out more closely to how they may be used in the real world and the differences between them is likely to become more apparent.
Low volume playing will have an impact on your results but not so much so that they will sound alike with an approach like that outlined above. I have several different monitoring solutions (a pair of active CLR's, a pair of active nearfield monitors (Equator D5's), and several headphone sets (Beyerdynamic, Philips, Audio-Technica, Sennheiser) including in-car's, and several different amps that I use to drive the phones. I mostly play at a fairly low volume (level) and occasionally play loud just because it's fun, or to take advantage of the interaction between the strings and speaker when recording (and when feasible). Most times low volume keeps my family happy so low it is.
I have the advantage of having owned many of the vintage amps modeled in the past, more often than not at the same time as I was collecting (and making use of) vintage tube guitar and bass amps so I've had ample opportunity to hear many of them side-by-side. Some Fender Blackface amps sound quite similar in voicing but begin to differ when they start to break up (difference in output power, rectifier type, speaker type/size, fixed or variable mid frequency, presence or no, etc. are all potential factors). Tweeds differ one model to the next for similar reasons. Vox amps, Marshall amps, etc. - the same is true.
You'll certainly notice more difference in greater detail at higher volume but the differences should be quite discernable at all but the lowest monitoring levels.
Then there's 'feel' or response. This characteristic alone can alter how you personally interact with any given amp. You'll likely find that you have a preference between slow and fast response, between a tight and loose/spongy feel, etc. Some folks just use these varying characteristics to their advantage based on the amp they're playing through.
I can tell you this; the differences between the various amp models in the AxeFX II are definitely apparent, and quite accurate as well - even at lower monitoring levels - when the amp models are set up and used as are their real-world counterparts.
As others have already noted using the same preset, same settings, same cab IR while rolling through preamp types will yield results so similar it wouldn't be worth the time spent. Likewise, rolling through different amp models with the same settings and the same cab IR will yield very similar results with potentially more difference in feel than in audible differences. It may seem counter intuitive but comparisons with common variables in place (master, gain, tonestack, and cab IR) will yield results showing far more common ground than different.
The right cab IR will make all the difference in the world. For an example build a basic preset with a Fender tweed Bassman amp (stock settings across the board) and two cab blocks in parallel. Load one cab block with a Bassman 4x10 and the other with a 4x12 loaded with greenback celestions). Set both cab blocks bypass to 'Mute Out'. Set scene 1 with the Bassman cab active and the 4x12 bypassed, and set scene 2 with the Bassman cab bypassed. You should be able to note the difference immediately where the tweed Bassman only sounds like a tweed Bassman when played through the Bassman 4x10 cab.
You could take this one step further by adding a second amp block in parallel with the first, both with bypass set to 'Mute Out', and set the second amp block up with a Marshall JTM45 with stock settings. Set up 4 scenes instead of 2, with each scene covering the 4 possible combinations (Bassman amp w/ Bassman 4x10 cab, Bassman amp w/ Marshall 4x12, JTM45 w/ Bassman 4x10 cab, and JTM45 w/ Marshall 4x12). This should highlight the differences between the Bassman and the JTM45 when each is paired with its own cab while showing just how similar the two amps sound through the same cab IR. I picked these two amps specifically because one is a circuit clone of the other with DC coupling capacitor manufacturer, transformer manufacturer, tube types and manufacturer, and output impedance differing.
I didn't think to ask until just now; What are you using for monitoring (nearfields? Brand/model? Headphones?). Consumer monitors are all over the place. Some have enough of their own color/character that they will tend to blur the lines further supporting the perception that all amps of a similar gain level sound similar. Though I was able to differentiate between the various amp models when I was using a pair of KRK Rokit 5 powered monitors many characteristics were somewhat indistinct. When I replaced the KRK's with the Equator's those vague differences suddenly became quite clear and distinct.
Your mileage may vary, of course. Given that you already own the AxeFX II and less than pleased with your observations indicating that models sound too similar. It costs nothing to take a different approach. If you have any reason to suspect that your monitors are contributing to your expressed observation then look into running the same comparisons through a borrowed set of nearfield known to have a relatively full frequency / flat response. If you don't know anyone with quality nearfield then ask the forum here if anyone in your area would be willing to host a demo.
