None that I can think of. I just run my out of my AX8 into return on the Fender. This bypasses the front panel of the amp and allows my AX8 to run the show. All I'm using the Fender for is the power section and the 2x12's. If your sound doesn't sound good, you'll need to tweak your fm3.
Only tips I can give you are these: You can't use a studio sound you love in your amp. You have to create a sound specifically for the Champion and its speakers/power amp section. What I suggest is, if you have a studio sound you love, you can try it and tweak it so it sounds good through the Champion. I have always created separate sounds for live and studio. That said, I usually use the same stuff like modeled amps, effects etc. But the sounds are drastically different than my studio tones. You'll need more bass in your live tone, but be careful not to use too much. Especially in the 80hz and below area. If you feel rumble, you're using the wrong low end for your tone. It's ok to feel a little something, but we as guitarists always seem to go for that "all alone sound" which is, the sound that sounds great all by itself but sucks in a mix of other instruments.
You'll also need less gain than you normally use. Those speakers break up quite nicely so you can use less gain so if you use high gain, it would sound like a run on sentence that's tripping all over itself. You'll also use less effect levels. The reason being, you'll lose sight of your sound with too much verb, delay or chorus going on. It's different than what you get in your studio. You'll see what I mean when you mess around a bit. You'll notice if you're not careful, effects will wash your sound right out and sort of mask it. You don't want that. Just be careful.
Experiment with your cab sim off and on, Sometimes off is the better option but it depends on how your IR's get along with the Fender speakers. I have my own IR's that I made, so they sound pretty cool in my 25 watt Greenback cabs as well as whatever those speakers are in the Champion we have. I'm actually quite surprised at how good that little amp sounds. You can't beat it.....2x12, 100 watts for under $400! And, if you plug straight in, it sounds great too! If God forbid my AX8 died, I could plug right into that thing and get a killer tone. You can go from Van Halen to Metallica in one click. I hope some of this helps. Good luck!
AX8 and Champion