Will an entry level tube preamp help w/ B&K ST-140

I have two B&K ST-140's driving 2CE speakers using a rotel tuner pre-amp. Good system for my investment. Would it be recommended to go with a decent tube pre-amp to play off of the already tube-like sound of my amps? Looking for even more detail and 3D sound stage.....thanks
Do you mean Vandersteen 2CE? If so, I have been using a Tube Audio Design-150 by Bizzy Bee audio to drive my 2CE sigs. I had an ST-140, upgraded to the reference 4420 then to the McCormack DNA-1. The B&K to McCormack transformation showed me that I was missing some of the music. The tube pre created the wide and deep soundstage...

My personal recommendation is to consider some other solid state amp than the B&K. B&K uses MOSFET transistors in the output stage, which tends to make them sound rather warm and soft. A better idea, IMO, would be a SS amp that uses bipolar output transistors. Most of the top SS amps use J-FET transistors in the input stage (very linear for low level signals), MOSFETS in the gain stage, and bi-polar transistors in the output stage. In the systems I've heard that use a tube preamp and a SS power amp, the SS amps with bipolar output transistors have tended to sound best -- better bass control, better dynamics, and more transparent.

My comments are not intended in any way of "slamming" the B&K product line -- they make some excellent gear. If you intend to keep your tube preamp (which may be a good idea), then I'd make the switch to another power amp.
Do it. I'm glad I discovered how much a tube pre can help a system sound better. As a matter of fact it's hard to think of using an SS pre again. You'll find that the tube pre will take your system to another level over the Rotel pre. You can get varying amounts of "tubeyness" from different brands, something you may want to consider as I tried a Cary AE 3 and it was just too syrupy where the ARC LS 16 added just enough tube sound to make it wonderful. I had the Vandersteen Model 2's and suspect that with a tube pre you're in for a nice sounding combination. Your amp could be upgraded at some time but I'd sell the Rotel and get a used Conrad Johnson or ARC pre. These can be found for 5-700 in good condition. You really have nothing to lose as if you buy used gear here you can recoup at least most of your money, maybe more. You won't be wanting to sell it though, you'll get your more detail and 3d sound and it will also be smoother and more natural sounding.
I used to have the SS Revelation Basic (dual mono) with my B&K and loved it... then I moved to an ARC LS-7 and waw wowwed! That was many generations of equipment ago & I still have a tube pre (Supratek Syrah) and SS amp (McCormack DNA 0.5 Rev. A by SMC)...
My experience is pretty much what everyone else has experienced. Once I tried a tube pre-amp I never looked back. My wife even commented how great it sounded and she doesn't give a rip! I started with a Conrad Johnson PV10a and eventually migrated to a CJ Premier 17ls then onto a CJ Premier 16lsII. I have only had experience with CJ so I can not comment on other manufacturers as others have. My experience has been and others have commented that the combination of a tubed pre with ss amp really provides a wonderfull three dimensional sound stage with very good bass control.

A Conrad Johnson PV10B can be had used on this site for around $500-$750. If you don't like it you can always sell it and move on and not lose much if any money; which is a great thing.

Good Luck and just enjoy the music!

A tube preamp should always be used with a solid state amp in my opinion as the solid state amp delivers the power and control while the tube preamp imparts a very nice musicality. For me this has always been the best combination.
It is my understanding that both Vandys and B&K could be placing your in the Yang-side of the audio resproduction spectrum (read: SOFT), why not try a passive preamp?, (could work great in your setup adding more resolution, transparency and speed).