Tube Rolling Quicksilver v4, Preamp recommedation

I've got a quicksilver V4 with Stock KT 88's. I wanted to experiment with other tubes to see what it sounds like. I've thought about some EL34's or upgrading the KT 88's. I'd like to hear comments.
I'm also considering a tube preamp. I'm currently using the pre-out from a YBA Passion integrated. It sounds pretty nice, but was curious what a nice tube would do.
I had a pair of V4s and usd them on the MR/tweeter panels of Eminent Tech. 8s. I used both the original Chinese '88s and a set of Ei KT90s I already had. Frankly, not being a GEA and being more of a tin-eared audiofool, I couldn't distinguish differences in their sounds, altho I'm sure some existed. If I were to buy new OP tubes for it, they'd be the solid-plate Penta KT88SCs that are getting raves on the Tube Asylum. On frontend tubes, I bought and tried MANY-different ones, but, again, couldn't distinguish between their sounds. I still have LOTS of 12FQ' and 'BH7s; e-mail me at jeffreybehr(at)cox(dot)net if you'd like more info; I'd love to be rid of them.

BTW I improved lots of parts in the V4s and improved its sound quality, mostly in clarity, cleanliness. Let me know if you'd like that info.
I own a pair of QS MiniMites (a bit different from the V4s I realize) and can say that I've found a very nice combination of driver/powers tubes in NOS RCA 12AX7As and the SED "Winged C" EL34. With the RCAs, I've done prior extensive listening to Tesla E34Ls and the new Electro-Harmonix EL34s. The Teslas were not bad (a bit uninvolving in the mids) but of nice build quality. The EHs were immediately different, w/very clean and detailed bass and mid-bass, a somewhat lean midrange, but too much treble energy (w/my Spendor Classics). Cymbal crashes and hi-hats called attention to themselves. The SEDs are the best of the bunch IMO: excellent balance, no fatigue, and w/more midrange body and harmonics than the EH or Tesla. I knew they were superior w/i 10 seconds of Chopin. Once you dial a good tube combination in, the Quicksilvers are really amazing. After MUCH research on driver tubes, I gathered that there is an overall concensus on the EH brand having more treble energy than Tesla or SED, and my ears told me the same thing (before I started researching!) I'd also consult w/your dealer if you can.
I would give Mike @ Quicksilver a call, as he will be more than happy to give you an "impression" of what to expect with different tubes.

I ran my V4's with Ei KT-90 Type III's. Very linear, good bottom end control, liquid mids, not as warm as the KT-88's. Each amp was tested at 170 wpc configured with the KT-90's when it left QS production.