Hiya Grant,
The Amplitrex is a nice unit. I noticed it has a 1/4" headphone jack for listening for microphonics. You should be able to solder up a 1/4" jack assembly that will let you clip your meter onto it and you can start to get actual measurements in mV of the noise associated with a given tube.
The trick is knowing a finite reference point where a tube becomes too noisy for given application (pre, phono or gain). This will take some time trying tons of different tubes to come up with that reference point. Once you do, then you'll be able to better rate or match your tubes.
I've got a Tripplett 3423 that I use. I personally find it is better than the Hicock's or TV-7s because it not only tests for noise at 60Hz but also 120Hz. It gives me a truer read on a tube.
Enjoy!
