Having recently solved my problem with getting a decent sound out of my X3 Live with the Spider IV 30 amp, it came to mind to share my setup here in case anyone else shares the same problem (X3 Live's sound being mushy, too gainy etc. with amp). My apologies if there happens to be a dosen posts like this one already, but here we go:
For starters I selected the clean channel so that the light turns red (so that the amp isn't modelling anything), then adjusted the knobs as follows; Drive 12 o'clock, Bass 12 'ish, Mid somewhere between 10 and 11, Treble somewhere between 1 and 2 (or 13 and 14, if thinking in 24 hours terms instead of a.m. and p.m. ), Channel vol 2 (or 14), and finally because I live in a flat with elderly people as neighbours I have the master volume at 8 or 9. (I don't use the modulations or delays from the amp etc.). Also I have the inbuild noisgate "on".
Now from the pedal I have selected as the output the "combo front", with lows and higs flat and the focus as 1,15khz. As for the channel volumes I tend not to crank them up to full (I keep them at say... 60 and 70 depending on the model and cab), but instead I switched the Live out switch (near tone volume) from "amp" to "line" and lowered the master volume (again because of where I'm living) to 11'ish.
Finally when selecting models from the pedal I leave it up to you to adjust the finer settings (bass, treble etc.) to your personal liking. A lot of the models have an insane amount of treble and bass selected (at least in my opinion), so you might want to lower those at least.
I would also welcome suggestions and tips from other people on how they've setup their X3 Live with a similar or same floor-amp.
Hope this helped someone!