high gain or low gain tube preamps ?

You have raised an interesting question on a complex topic that probably has no correct answer.

IMHO, most systems have too much gain. Many of today's amplifiers have close to 30 db of gain; so adding another 20 db in the pre-amp is too much.

Even in a system with lower sensitivity speakers, a total system gain of 32 db is sufficient in most rooms. So, 26 db in the pre-amp is overkill (again, IMHO) and may just contribute to more noise being amplified in the power section.

WEEZ

Well the appropriate pre-amp gain depends on the source that you are using (how many V does have the signal that is coming in) and on the power amp that you are using - how much gain does it produce.

If you are using a CD player with 2 V output (nearly a standard nowadays) and you have power amp with 30 dB gain then you do not need huge gain from pre-amp. Several dB will be sufficiant; let's say 4 dB or 6 dB. If you are using a source with lower V output (tuner, ...)and you have an amp that has 20 dB gain, then it may be necessary to have pre-amp gain of mentioned 15 dB.

So it has to be judged in the context of one concrete set-up. I do not believe that there is a generall answer on your question. There though pre-amps that have adjustable gain (Pass Labs X 2.5 is one of them) so you can change the gain level in the pre-amp. This brings additional flexibility to the pre-amp and is certainly interesting feature.

Regards
Dejan