I've been working with Fractal amp models and Cab IRs for over ten years now. My informed opinion is that there are three main issues for newbies to getting that elusive "amp in a room" sound.
First, they don't have a great FRFR playback system. You are not getting to get a 4x12 Marshall "amp in my room" sound on a preset coming out of a little 8" stereo monitor. A
good FRFR Monitor - the good ones aren't the cheaper ones -- is the solution. I'm partial to a one or a pair of Atomic NEO CLRs myself, but I now have a Mission Gemini 2 2x12 that is growing me on too and really sounds like an amp!
Second, newbies often do not gain stage and level their presets and the hardware settings for audio output properly. So the sound may actually be great BUT it won't sound right if the level is too low for playback (or too high).
It's weird when you first discover it, but I have dialed in presets that were simply "uninspiring sounding" as I turned the amp LEVEL knob -- until all of a sudden --
bam - at the right db level, it all clicked and filled the room with a great balanced sound.
The Fletcher Munson effect (Google it) is a real thing. If you want an amp in the room sound, you have to play as LOUD as an amp in the room to get there. Not horribly loud, but at least at -92db (get a db meter App on your smart phone) so the Fletcher Munson effect does not play tricks on your ears and fool you.
This is why presets dialed in at bedroom levels and may sound great played low at home, but all of a sudden sound horrible at your band practice or gig -- too much lows, too many highs, not enough mids, etc. The guitar is a MIDs instrument, and the juicy meat of the electric guitar is between 200Hz to 500Hz and the other definition is the stuff between 500hz and around 2.5kHz.
Last, I am more convinced than ever after 10 years that finding and using the RIGHT CAB IR IS ESSENTIAL to getting a great sound for live playing. Unfortunately you have to really search -- 90%+ of IRs available will not work well - based on the mic used and position, there are not enough or too little bass/mids/treble for a good live sound (but can work for a recording or mix though in some cases).
Lots of people use the Royer 121 and SM57 mix and it can work if the IRs are captured right. But my favorite guitar mic/IR is the Beyer Dynamic M160. That's the key mic Eddie Kramer captured all those great Hendrix, Page, and Stones guitar tones on (blended with other mics and treated further at the mixing board to be sure).
I find that if you can locate a perfect M160 Cab IR capture, that alone is all you need for most amps. I usually start looking at those, then the Royers, then blend an SM57 in if it needs some further "bite." The M160 blended with an SM57 (with the SM57 mixed down lower) also sounds pretty great for a"live amp" sound through a good FRFR. I think our awesome resource and source of the Amp Wiki
@yek also discovered that mix recipe before me. (All hail Yek!)
Okay, one more thing. I have really been using the clean Amp Boost a LOT lately, not at the default +12db, but tailored to the amp, between +6db and +10db. It truly makes low and medium gain amps really get fat and juicy and come alive if you have the right IR and control the bass. That will take you to a happy place.
Enjoy!