As you know, the K701/2s & Q701s require an Amp that can provide sufficient current and voltage, and a couple of pre gain settings are surely welcome to get close to the sweet spot of your match. The Q701 needs 3.2 Vrms, that's 4.5 volts peak; At 62 ohms, that's 72 mA of peak current. So the Q701s need a low output impedance and quite a bit of voltage and current. IMO, that's the equation you have to solve first. Once you got a list of the tube Amps that match those characteristics, you can make the money math. Saving a bit more and waiting to get something better always pays off.
This is quite frankly...insane. Way too much voltage. About ten times. You're over their max input by a decent bit too.
From Tyll's measurements, ~1.65mW/ch:90 dB SPL. That's around .3Vrms @ 60ohms. The 701 also are fairly stable, so the concern over low Zsource is somewhat misplaced as well.
From AKG's specifications, they're some 100-and-change dB/V (note V). Which means that .2-.4Vrms range is pretty on-target.
I lol'd @ the 336 dB point - that's a few million times the atmospheric limit of acoustic pressure (which is around 194 dB; 40 dB of gain is around 100x loudness, you're talking around 150 dB of gain on top of a sound louder than a volcano exploding - I think that's *almost* loud enough to properly enjoy KISS).