Pre-amp suggestions for Thiel 2.4/Pass Labs XA30.5

A Chinese amp with an unusual tube, that will put out less power than the amp you currently find to inadequately power the speakers your driving? Good luck with that!

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Ha... well, I see you have a strong opinion on that! I thought I was comparing 60W (the XA-30.5 into 4Ohms) to 160W out of the EE. Still learning how to compare amp output though...

As for the Mac, all I read about was the response into varying loads from a single tap... so the way I read it, from any single output, they will double down in provided Watts as the speaker's impedance drops by half (i.e., goes 4 to 2 ohms).

Here's a quote from a discussion about Mac autotransformers:

The output autoformers have different windings in them so the 2,4 & 8 ohm taps are like 3 different amps that are optimized for speakers with the corresponding 2,4 & 8 ohm resistances. If you have a MC501 rated at 500 watts and you hook up a 4 ohm speaker to the 8 ohm tap you will get the expected 1000 watt output (maybe a little less). This could cause the amp to go into protection though, it is usually best to match the speakers to the correct tap.

http://www.audiokarma.org/forums/archive/index.php/t-71322.html

As you know the 60 W @ 4 Ohms of the XA30.5 was the Class A output, the XA-30.5 would actually put out another 130 or so Watts in Class B @ 4 ohms for a total of about 190 Watts @ 4 Ohms.
I really am a bit confounded by the ss Macs. Perhaps I'm mistaken, but I thought the use of autoformers prevented doubling down into halve impedance's?

Good link! As far as I can tell from the discussion the ss Mac will only double down if the tap used is higher that the actual speaker demand, and that to preserve the amps stability that is to be avoided. To prevent the amp from being over stressed they use an autoformer with multiple taps, with the idea that one should use the tap that comes closest to the speakers load (I suppose that might be an issue with some speakers with wide impedance swings, the Thiels don't). When used as recommend the amp should not double down and therefore with lower impedance's would have lower dBW output. I could be wrong, but this would appear to be a high powered but not especially robust (in comparison to some other high end ss amps) amplifier design. If I'm mistaken, please anyone enlighten me.

"but I thought the use of autoformers prevented doubling down into halve impedance's?"

That what I thought, the point being that you would get more linear/constant power output throughout the bandwidth without variances caused by impedance swings.