I'm using a VanAlstine Super PAS3si (modified by Tom Tutay). Toms mods opened up the Super PAS3si and extended the top end without any brighness. I also got a wider soundstage and deeper soundstage as a result of the mods.
The original unit replaced an Audio Research LS9. Loved the remote but 6 db of gain wasn't enough for my Dynaco ST 70 (Sound Valves input board also tweaked and modified by Tom Tutay). I have owned the ST 70 for over 10 years and have had various updats done to it.
Before the Audio Research I owned a Croft Vitalie and an Audio Innovations P1. Both were excellent units. Actually the Croft was superb. I got an offer I couldn't refuse on it and sold it.
The VanAlstine Super PAS mods (Dynaco PAS3 based with VA mods) are excellent units too. They have a similar circuit to my VanAlstine Super PAS3si which was a VanAlstine original circuit. The Stereo 70 does not have
any problems with the preamps I have used including Audible Illusions 2 (c or D oo much gain for me but excellent for some systems). Conrad Johnson PV5. Very good but I would opt for the PV10 or the Classic instead. My favorite vintage pre is the PV7 and the PV9. The PV 7 may be an excellent choice if you can find one. All of the Counterpoints work well with the ST70. As I said there aren't many solid state or tube units that present a problem for the ST70. If you understand the sound signature of the company and the preamp you are pondering then you will be okay. Yes, each company has it's own sound signature. A Rogue 66 was horrible with my ST70. But it was a very eary unit and I didn't want to pay $250 to have it upgraded. It lasted 1 week. PS Audio 4H, 4.5 or 4.6's all work very very well with the ST70. All the preamps I have mentioned I have owned or listend to IMOS.
One last thing if you have a ST 70 get the input board upgraded. There are many out there today. The Dynamutt or the Triode or VanAlstine as well as Curcio, KEnnedy and several others. I really like the Octal tube mods I have heard lately from RustnRot. He is an electrical engineer and he does great work. He is located in Augusta, GA. Not well known yet but I have heard his amps and they sound great.