Itching to upgrade preamp...

I would look seriously at the PS Audio BHK pre BUT you have to get different tubes.  The stock PSVanes were horrible.  I had NOS Tunsgrams that were amazing.  

It is balanced, will come in on budget with the trade or below budget if you buy used even with the NOS tubes.  
I upgraded from the BHK but my system is entirely single ended now.  I was using VTL Monos and had the DSD with Bridge II.  
I run all Art Audio gear (I am the importer) and moved to Chord for my digital.  My Conductor is 100% a better preamp in a single ended system than the BHK but in yours which is balanced, the BHK will be pretty great. Another perk is that it uses the same remote as the DSD. 
Two other options, the McIntosh C22.  Brilliant pre and it just is begging to have a turntable added to it.  The phono stage is obscenely good.

The ARC LS27/28...whichever you can fit in your budget.  Darn good preamp for the money and would work supremely well in your system.  
I have run the DSD direct into power amps previously and found it to be a significant step down in quality from a separate pre.  

I used to go direct from the DS Sr to the XA60.5, but inserting the preamp added quite a bit more space and drive.

Sorry but it’s impossible, for the XA60.5’s 1.1v input sens, 30khom input impedance to "load down" and reduce the "drive" from the output of the DS Sr’s 3v 100ohms output impedance. All a pre can do in this case is add coloration/distortions, as well as the extra set of interconnects
Even Paul McGowen has said so  "The ability to eliminate the preamplifier in the system without any resolution loss is a major benefit to DirectStream’s outstanding musical performance."  

Going through the P12 the XA60.5 yes it looses a bit of low end slam

And this is telling you something that Nelson Pass would even object about.

There are other things you need to look at "if" both these so called apparent "fixes" are better to you.

Cheers George

The Luxman CL38U C is in this price range. The late Art Dudley rated favorably w/his Shindo. It was also rated Class A on the Tube Preamp listing. A big bonus is the phono section. Worth auditioning, if you can.

I am with georgehifi, on this. Passive is the way ( has been for me ). However, I understand the addition of a gain stage / extra circuitry, with the " drive ", " color " ( could be distortion ), that people like. It is all about " what you like ", as there really isn't a right or wrong. Besides, all of this, is quite dependent, on the particular recordings we listen to. Some, admittedly, can use some help...others, not.

How far are the fronts of your speakers from the back wall?