Hey j4q0,
I have the Classic also which is my favorite preamp of all of them. I don't have a lag in mine when it comes to channel switching. May I suggest you check your MIDI program change assignments in both your controller and the Classic? I do not use the Omni mode for program changes, (all 16 channels), I assign and match each channel to each unit I'm sending to, and I try to avoid MIDI mapping whenever possible.
I agree that the frequencies in the Classic are not as broad as the original MP-1, but going with long plate good quality tubes will help that out a lot. I also have the MP-2, which I've done a lot of tweaking to, but even so, the dynamic response in the Classic still beats out the MP-2 hands down, (IMHO). I've tried a pair of GT 12AX7R-2's in the Classic and found the low end was boosted a bit more in it, but the GT's didn't last very long. I also tried a pair of the Russian made Mullard RI's, and they didn't last either. Good results, but short tube life. Currently, I have a pair of JJ ECC803's in there, and I'm liking what I'm getting, but I'm still experimenting with other brand names. I may try some Pentas in there next since they are kicking my original MP-1 in the a$$! They are a bit pricey, but good tone is worth it to me.
Check your MIDI settings carefully, and get back to me on that one. I'll go review my owners manual in the meantime and see if I can spot anything else in the MIDI section which may affect the program changes.
Harley