At 60 watts, the Vintage 30's have a lower breakup threshold. Additionally,
they are a little warmer than the G12-80's, IMHO.
Another contributing factor to the excessive brightness problem might also
be your tubes. Try replacing the preamp tubes first with some Sovtek
12AX7WBs. I've found these to be extremely warm sounding. TIP: Order one
or two more than you need (they're cheap) so you can return any that are
dead out of the box. The ones that test out good will last a long time with
good tones.
I remember reading the initial review in GP about the Tonemaster. Their
concern was that it was way too bright with anything other than the
Vintage 30's. In their rebuttle, the boys at Fender admitted that
they voiced the amp with and espescially for Vintage 30's. GP
concurred that the V30's warmed the amp up quite a bit...
Thanks Perry