What to update first: pre or power amp?

Source first. If you don't have a good pre-amp, your amp and/or speakers (no matter how good) cannot make up for information that does not get to them. This has been proven, although some will undoubtedly disagree.

preamp and speakers are top for me...

I had a Magnum 88 and went to Magnum 120s and there was not a big difference. My point is, I am GUESSING the M88 is a better sounding piece than the M66 pre and therefore agree that you should get the pre first.

There is the argument that since the power amp controls the speakers you may want to upgrade that first. Especially since you have tubes and they do not always control the bass that well, however, The M88 controlled my Maggie 1.6 quite well and is a fine amp so stick with getting the new pre.

all the best,

Phil

keep the pre you have and get a more powerful rogue amp. the martin logans need gobs of power, and although most goners seem to prefer cj over rogue, i think the synergy between two quality components of the same family give you a system where the whole is greater than the sum of its parts.

I had the 88 and went to the M120's and saw a huge improvment. It just goes to show you that 2 people can do the same thing and not have the same sense of change.
I think the 88 is not a very good amp. I would switch amps first. And as soon as you can afford. Change the pre.