When I bought my Axe FX II a couple months back, I too thought I could just use it as a Preamp, who needs modeled amps and cabs when I have the real thing? I promptly rewired my rack and tried it in many a different configuration, including power amp inserts in my 2 Marshall 100 watt heads, I tried a few different SS power amps, but it always sounded the same because of the Marshall cabs. Tone matching didn't translate AT ALL, and the amount of tweaking required.... forget it......
I didn't really understand the concept as I have been a Marshall full stack guy for 25 years. I spent many hours just trying to dial in a couple basic tones and yes I got some ok tones, but it wasn't until I started renting some FRFR powered wedges and using Amp Sims and Cabs PROPERLY did I see what the Axe FX was all about. Finally all those video you see on youtube with those fantastic tones, using FRFR I now was able to get the same awesomeness with 100% consistency.
I've now gigged with a single Yorkville NX55p for the last seven shows and it's a game changer. no longer is there the "cone of deaf" when standing in front of my 4x12 full stack, no longer do I need to mic and hope the settings on the board are great, as I am sending the exact same feed to FOH and because I am using an FRFR speaker, the translation out of FOH is nearly identical and it sounds amazing, clear, punchy, and best of all cuts through the mix perfectly and has ZERO muddiness.
2nd, all the powered wedges in this range have a built in mixer with 2 inputs so I use one for the Axe FX and the other for the vocal mix from the board. I am really enjoying it and while the Yorkville isn't the best out there it definitely holds it's own. I am now on the waitlist for Atomic CLR active wedges, and I think I will be set from there.
I am not saying you should ditch your Marshalls, but just have an open mind, and if you can rent a powered wedge in $850 - $1000 range, rent one for a month. you will see. Pretty much any of the commercial brands (JBL, EV, QSC, MACKIE, YAMAHA, YORKVILLE, ETC) out there in this price range offer the same specs and performance. Rental for my Yorkville is about $35 for a month.