Tube info

The M125 monoblocks...
http://www.tubes4hifi.com/bob.htm

There are indeed only 2 driver tubes on each monoblock. If I’ve read this correctly, the driver stage generates higher than typical voltage, so there isn’t a separate gain stage.
The sonic effect of the driver tubes will be significant.

I've been using those expensive high test Mullards from Upscale for a while now.  Conrad Johnson PV10 tube pre-amp with ss monoblocks and the KEF ls50 with REL T5 subs.  The mullards sound good in this application because they smooth it out a little.

This is really great info. Thanks guys!

Have you decided on power tubes?

My experience is that they can make a bigger difference than the smaller tubes.  You can fine-tune your sound quality by mixing different qualities in the power tubes and the driver tubes.

FULL DISCLOSURE:  I occasionally sell tubes from my personal collection.  I can post a listing here if I have something that interests you.

I have several power tube options available, again depending upon your budget.

The premium European 12AU7s will likely be above your $30-$40 each budget.  The US options should be well below that.

 My experience is the opposite, the driver Tubes tend to make more difference when I’ve tried them.