Is there such a thing...

as an KT88/6550 based tube that sounds similar to the midrange of an 845 tube? I was listening to a friends setup that uses the Unison Smart 845 amp and was blown away by the midrange. Is there any way I can come close to this sound without buying a 845 based amp and high efficiency speakers? More specifically, what 6550 based tubes, interconnects, etc.

Take a look at my updated system and tell me what you think.
There is more to it than just the tube, I'm afraid. Single-ended topology has sonic advantages over push-pull topology.

What are the efficiency and impedance (minimum as well as "nominal") of your speakers? Some 845 amps are specifically designed to work well with medium efficiency speakers.

The overall sound comes from the combination of all his components, not just the 845 tubes. What speakers does he have? What is the rest of his system.
My speaker specs are:
Response: 28 to 22 khz Efficency: 89db
Power: 40 to 300 watts Imp: 6 ohms
They may drop down to 4 ohms if driven hard but I rarely go past 10 o'clock on my volume pots.

His system consists of:
Unison Smart 845 monoblocs
Von Schweikert VR4
Joule Electra LA-100 pre (I think)
BAT tube cd player
Mostly Synergistic Research i/c's
The specs on your speakers are not that much different than his. Can you try his amps in your system?

I doubt you get the same sound with a push-pull pentode amp vs. an SET amp like his.

FYI the impedance of your speakers is unrelated to how loudly you play them. It varies with the input frequency but not the power.
I agree with Herman's suggestion that you give the Unison amps a try on your speakers if possible. Your speakers are certainly in the ballpark.

There are many 845-based amps that I'm not familiar with (the Unison being among them), but among those that I am familiar with I think there are several that would work well with your speakers, assuming you aren't looking for rock-concert SPL's.

Herman & Duke
Your insight is greatly appreciated. I think I'm just going through denial.

I know the 845 will be able to play my speakers but I'll be giving up a little bottom end for that midrange I'm craving. I told myself that the Aronovs will be my last amplifier, they did everything I wanted them to do until I heard those 845's.

I'll see what I can work out with my friend or maybe see if I can find a pair at a local hifi shop that I can demo.

Agree, there may some things the 845 SET amp does, but at a compromise on other things. Such as how are the bass/highs compared to my KT90 amp? Besides will the 845 amp deliver the same soundstage on my Thor speakers as my KT90/push pull? In all things audio, there is compromise. From what i know the KT88 would be close to the 845 in the mids. But then expect more roll off in the highs/bass vs the KT90 tube. I've heard the KT88 in 3 auditions and didn't care for it.