The Sig X is a amp I use a lot ..... it is my favorite multi-channel amp. I have several others ... but it is by far the one I use most. Build quality, definition, articulation, dynamics, feel & tone is all better for me. All channel's regardless of how much gain is being used can clean up great with the guitar volume. The controls on each channel allows you to really shape the sound. A ll three channels can do clean on up to crunch. The CLEAN channel driven into overdrive is one of my favorite crunch sounds from any amp. Both RHYTHM & LEAD can do clean thru high-gain.
The JVM is alright .... But personally I much prefer the JCM800 single channel & older Marshall's. I like several of the newer Marshall's .... But the old single channel amps are much much more to my taste.