Tube Pre and SS Power? Or the reverse?

Either all tube or all ss, I see no reason to mix. Unless you don't want to deal with many power tubes required for some serious power. But that Chinese stuff they now put in is available and relatively inexpensive, so it should come down to your speakers. If you do mix you will get a transistor sound, anyway. Makes no sense to me.

Tube preamp

Tube preamp and SS amp.

However, in my investigation into flea watt SET tube amp Sonics and some tube rolling, I’ll try to find a neutral preamp which will likely be SS.  

I had a tube preamp with a moderate powered solid state stereo amp and went to tube stereo amp …. Resulting in loss of detail and sound stage.  I went back to a higher powered solid state—mono bloc Odyssey Kismet in less expensive cases—and the result was simply superb in terms of sound stage, resolution, and even tonal qualities.  I am now considering a preamp upgrade, and whichever I choose, it will have tubes.

I owned MC275 - it’s ok, but not amazing IMO.  All McIntosh gear uses too much global feedback.  If I was to choose from the above I’d go for the MC462.

I’ve tried loads of pre and amp combinations.

Most solid state amps use too much global feedback and have too complex circuits to let a tube pre really show what it’s all about.

I’d say go integrated hybrid tube amp - look at Pathos.  Way way better than MC275.