Hi Michael, I've been using an older Allen & Heath model...GL 12 ? I was very happy about its sound result so that now, using a switchblade i miss it a little. I was entering into the channels bypassing its preamps' section (using the inserts), this allows you to avoid too many gain stages that would result in a very difficult success in finding where, in the signal flow, you have overloads (i was using auxes and groups sends a lot to feed the processors, so there were 2 more gain stages there). Consider headroom and, also, consider ergonomy. To be able to switch sends on/off, to route a signal to another processor and so on in an easy and fast way, is a very important thing when you start using mixing as an instrument by itself. Sound is a matter of taste, so the best to do is test each mixer with your gear and monitors. I didn't understand if you are comparing the sound with/without mixer in between you amp's send/return or if you're using the mixer after the amp's send and then you go to some monitors. I agree with Kim when he says that deep-looping drives a lot of us gtr player from classic amps to full range monitors - and when you do this step, you find that gtr sound through a full range monitoring is a different world, you have to start thinking to sounds in a complete new way. hope this helps a little bit. don''t give up trying with mixers. luca > But, the rack mount mixers I've tried so far, an early Mackie CR 1604 >(not > the VLZ or Pro), and an Allen & Heath WZ 16:2 seem to color the sound in a > non musical way, IMO - at least in a non guitar friendly way. My guess >is > that it is the mixer channel pre amps. Even the reverbs and delays sound > different than if I just threw them into the amp's effects loop - very > different - sort of harder, not as lush or as full.