Tube Preamp with Solid State Amp?

Haven’t heard from the OP for awhile. Fairly safe to presume that the Parasound gear predated the 4th iteration of the Cornwall in your system. I am by no means knocking Parasound, as I think they manufacture well-engineered solid state gear for a fair price. While I think a tube preamp with solid state is a great combination for most systems, I am not sure it is for the Cornwall. Dick Olsher famously remarked that “the first watt is the most important watt”. You will likely listen to no more than 1 watt with that speaker in a small to medium sized room, so it better be a good one, or the other 249 in the case of the A21 are a waste.  Do yourself a favor and either use the A21 for a second system (driving an inexpensive inefficient bookshelf speaker perhaps), or sell/trade it. Get yourself a flea watt single ended DHT (2A3/300B/845) amp and find out what Olsher meant and what you’re missing. 

I’m running a Manley Shrimp with a McIntosh MC-352 and the sound is wide and open. To my ears sounded better than my Mac SS pre.  I have alway enjoyed a tubed pre and SS amps. I also run it through a Primaluna Dialogue HP tube amp. Those amps are wonderful sounding.

After growing my audiophile hobby with a fair amount of SS gear, I too finally decided to go the tube route... because of the music I listen to, and the relatively small size of my listening space... I don't tend to listen at high volume, but wanted to get an "enveloping" sound. 

I was getting set to pull the trigger on a Prima Luna integrated, and surely wouldn't have regretted it if I went that route... but wanting to also invest in a much better streamer, I realized my budget was taking a beating... 

Then I heard about the Heaven11 Billy amp, and really fell for the simple form factor, and the swiss-army knife approach to having a lot of input options and built in DAC. With tube pre and ICE  D-class  amplification, it really works paired with my Sonus Faber Signums to bring both detail and warmth. With the savings the Heaven11 brought, I could afford a used Lumin D1, which was really the missing piece to the puzzle. 

The Schiit Freya preamp (now the Freya +) allows instant switching between tubes and 2 other modes so you can see what's what regarding the tubes, and the tubes sound snappier, more detailed, and provide what I take as a more accurate presentation...my older version is very quiet and amazingly well made and sounds fabulous. The lack of "crossover" distortion and transistor harshness is gone of course from my single ended pentode power amp, the result being a more accurate musical presentation. Nothing "euphonic" or "smoothing", simply detailed down to about 58hz where my 2 under stressed SS RELs take over.

aberyclark
So you want to tailor (synonym: improve to your ear) your system's sound.
I have a tube/SS rig:  a vintage Parasound HCA-750A amp with adjustable volume controls on the rear (75w/CH 8 ohms) running thru a little gem of a line level preamp (3rd owner; which I have for over 10 years now; supposedly only 10 hand-made) by Dave Wolze, an electrical designer in Calif, back in the early 2000s (says his partner withdrew, and it crushed his dream of production; his phono preamp appears to have been highly regarded as a kit). Speakers are giant 2-way bookshelf (?) JBL (funky cabinet) L25 PRIMO - AND THEY ROCK WITH THIS COMBO (CD only,tighhntly...) AND CAN PLAY LOUD MAN!!! (example Bohemian Raposody - We Will Rock You)
I'd suggest that in looking for a tube pre - the complement of at least 2 -12AX7s and 2-EF86 tubes is a good start...
AS A COMPARISON:  My Main System is a relatively new MONOPRICE INTEGRATED TUBE AMP (using Pre-outs and Main-ins) with a vintage YAMAHA discontinued HTA-5550 ( 75w/ch 8 ohms) into what I consider a great pair of sleeper bookshelf speakers - KEF Q1s! 
I am an extremely cost conscious audiophile (if I say so myself) and find as much challenge in sound improvement by science (understanding) and experimentation as enjoying the listening experience ( including the plethora of music, or so-called music, choices available) but my funds are very tight, so I continue to learn, try and keep what pans out... Try something cheap like the MONOPRICE Integrated with Pre-outs - probably about $150 or so, and see if you like the flexibility/change...
OR GET A VINTAGE MORRISON ELAD - and find out what your system really sounds like with a "Straight Wire with Gain"...
NO MATTER WHAT: ENJOY YOUR EFFORTS! Best Wishes. Bill