A tough challenge with highly efficient speakers and noise floors on tube amps.
On the humming, how have you set up the filament balance adjustment, Dubai2K? What I would suggest to start by shorting the MC-30 inputs and then adjusting the balance for least hum. Then, you'll be pretty much able to tell what the best case will be with the MC-30s from the hum standpoint. Make sure you leave the MX-110 disconnected from the amps when you do this to eliminate any potential ground loops.
2 things to address the noise floor:
Gain controls to minimize noise: You can lower the input levels at on the MC-30s while running the volume control on the MX-110 a bit higher. This may help the noise floor. Experiment with them to find the best arrangement for your installation.
Pinpointing the noise source(s): You can also use the shorted inputs arrangement to evaluate the first stage tube's noise factor in the MC-30s. Do this by substituting some other 12AX7s in its place with a pretty sensitive voltmeter on the output. Ideally this would be a spectrum analyzer or scope but those are pretty heavy on the pocket book. You can use your ears and those efficient speakers but it is hard to evaluate noise levels without some sort of objective measuring device - your ears really aren't - or at least mine are not! BTW, I do like the 12AX7LPS tubes for their low noise floor and use them in preamps and first stage power amp positions for that reason.
I expect you are also running a 3 pieces of gear through a step-down transformer, correct? If so, after all the above activities, if you still have aren't satisfied with the noise levels, and there's still hum, begin to think outside the boxes and look for ground loops between the devices including the step down transformer.
Hope that helps get things started.
Cheers,
David
