With Magnepan 20.7s I use a Bryston 4BSST² amplifier. Same time I bought the amp I bought Bryston BP-26 preamp.
Since then I have added VAC Standard (currently not working)
Conrad Johnson ACT2
Audible Illusion Modulus 3A
Before I bought the Bryston gear, I owned and still use Audio Research SP-15, and a Onkyo Grand Integra P309
So yes I have used all of these in my current system. And actually the ARC and AI are my current phono boxes.
Over the eight years since I got the Bryston BP-26 It has never been a bottleneck as I improve other aspects of my system. I would recommend a BP-26 anytime, and would buy it again without any hesitation. Used are about $2600 to $3000
If you have problems with Digital playback, a nice tube preamp is great. If you like clarity like a straight wire with gain, no better than the Bryston BP-26. Which BTW, is in TAS recommended components this year.
(I would recommend against buying a Audible Illusions anything. LOL)
VAC is good but really pricy, even used. (different models use different tubes)
Neutral on Conrad Johnson, the later models Russian tubes are getting scarce...