PSE Studio SL preamp, questions and comparisons

Hi all,

Love the site. I am looking for a little advice on how to step up from my current preamp, an NAD 1600. I just bought a beautiful PSE Studio IV amp here on audiogon. It's absolutely amazing and I intend to have it for a long, long time. I am driving NHT 2.9s so I may wind up biamping at some point but that's another story.

As luck would have it, there is a PSE Studio SL preamp available locally. The seller says he bought it new direct from Dean (the man behind PSE) in 1992. I have a couple of questions: 
- The unit has rack handles. I haven't seen another PSE with rack handles. Anyone know if this is a special unit?

- Also, there are no balanced outputs on this model. Other Studio SL's I have seen have balanced as well as unbalanced outputs. 

- On the inside of the unit, the PCB is marked "Rev. C". I have seen a few pics of "Rev. D" and the circuit does look substantially different. Can anyone comment on rolling upgrades in the Studio SL?

Finally, how does this unit stack up against more modern day competition? For example, a MUSE model 3 (non-signature) or a nice passive (the Studio IV seller told me the unit worked very well with passives due to it's high input impedance)?

Thanks all! Any comments are welcomed as it's hard to find info on PSE in general, let alone the studio SL.
The sound is awesome.  Rack handles were optional.  My SL had both but my IV amp was rca only.  Inside the SL some had updated phono sections (I believe they were gold plated connections).
The one problem to be aware of is interference.  My pre was great and no hum.  My amp was perfect with no hum.  Kept 2 feet apart they sounded awesome as a pair.  Tried stacking them, even on shelves and got tons of hum.  I sold them instead of trying to shield the heck out of them.  
Just my 2 cents...
Thank you Elevick. Are you saying that I should keep the AMP and preamp at least 2 feet from each other, even if they are on different shelves on my stand? In essence, should I have full shelf between them? 

Any cables you  recommend to help with possible interference?