Just recently started using an M-Pulse 600. I must say that now that I have it dialed in to my liking I am seriously digging it. I am playing it through an Ampeg SVT-410HLF right now and it sounds pretty darn good. The sound is very organic to my ears. Im using a P-Bass with an Aguilar preamp installed and I mainly keep it on passive mode for the most part. It seems as if the 5-band EQ can take me from an old school heavy mid sound to a hi-fi sound all with a few twists of the knobs. Im actually using the solo feature as a 'mute' by turning down the solo knob all the way on the amp and clicking the footswitch when I need to tune. Works pretty well. Anyway, anyone considering an M-Pulse 600 should check it out. And all the people that have given this amp praise in the past were exactly right!