Comparing the ET2 and the Classic SE is problematic because they are very different; designed for different purposes. The Classic is just that - a classic "no frills" preamp. No remote. Think of it as an updated PV-10B. The ET2 is a completely different design - more of a control preamp, intended for use in mixed audio/HT systems. I have heard both, not at the same time, but I would say that they have different sound qualities.
If I were looking for a preamp for a MC275 I would probably look at other options. In the CJ line: if you want tubes I think that the CT6 (discontinued) is a great bargain and (to me) sounds much better than either the Classic SE and ET2. But for use w/ an MC275 I would probably look for a good used Premier 18LS or PF-R. Yes, SS, but I think that the MC275 is already pretty warm and a bit noisy. A quieter preamp would be helpful.
Re: your other choices: I think that you are trying to add too much preamp to your system. The MC275 and 804S speakers are just not all that resolving, IMHO. Why not a good used Mac pre?
