new to tubes, match for spectral amp

I can't imagine mating any Spectral unit to any tube unit, amp or preamp. Besides, if you like Spectral, you won't like tubes, and vice versa; if you like Spectral, then any tube unit will sound slow to you. If you favor tubes, then Spectral sounds harmonically lean and spatially sterile. I'm a tube guy, so I'd replace both if you want to go to tubes. If not, stay where you are. Also, you have a package system tuned to work together and the the MIT, in particular, sounds best with SS.

Given the widely divergent musical presentations between Spectral and any decent tube gear, with due respect, I think you need to ask yourself why you liked Spectral enough to buy it (apart from the package MIT/Spectral/Avalon reason, assumably) and why you would now like to move so far away from that perspective.

I'm not being concrete (read: rigid), simply giving you my honest advice in a concise form. That you did not like its consequences in flexibility for your next purchase does not reduce my advice in the same manner.

Yes, flex, Eidolon is more harmonically rich to balance out people who buy SS, and particularly units like Spectral. The MIT does the same thing. At that, assumed, level of system balancing such divergent balancing in equipment profiles, in my humble opinion, is regressive.

This is an arranged system without the flexibility to move in as many directions as other systems because it designed to appeal to the audiophile who wants it done for him by a grouping of manufacturers working together in the first instant. This philosophy, while effective in the first instant, reduces flexibility thereafter. Flexibilty is not impossible, but tubes are incongruent with this system's balancing parameters. If the system still sounds sterile (even after the harmonically enhanced Avalons and MIT's...) then I would agree with the person who says to go with a tubed DAC.

Again, we need to know why the questioner finds his system needs changing and in what regards (a sudden move towards tubes assumes, usually, deficiencies in harmonics and spatial presentation, although the questioner never specifies this). Perhaps I wasn't being, er, concete enough in my first response...