Preamp pairing with B&K ST-140

Hello all:
I'm ending my mid-fi ways and entering the hi-fi entry level realm. I was recently blessed with a B&K ST-140 and I'm using it with a Newcastle R-925's pre-amp out. Sounds good, but I'm told if I upgrade the preamp I'll give the Newcastle away. I split time between a pair of Paradigm Studio 40's and Klipsch Forte's. The ST-140 will hang for a lil' while but I foresee replacing it in about a year???
Any input appreciated,
Before considering a tube pre, consider the relatively low input impedance and soft lower end of the B&K ST 140.
I owned and enjoyed the ST 140 for a while. I thought it was very musical and had surprising bass slam. I used a pre amp section of a NAD integrated and a McCormack ADL until I upgraded to a McCormack amp. Experimanting with a tube pre amp would be cool-maybe a used CJ PV-5 or ARC SP-6. They would give you a phono option too.
I 2nd Rrog's suggestion. I had a B&K Pro10MC Sonata paired with an ST140 for over 8 years before I started continually cycling equipment in and out of my system.
My local guru at Wilson's audio highly recommends ARC. He has a SP-7, recently serviced, but the $800 tag may be a little steep right now. I do want to minimize swapping components, as I can see you can spend more $ if you don't hit the right price point.
No oil in my morning coffee... yet,
Walter in New Orleans
I'm learning and was recently exposed to this. So you should match a preamp with relatively low output impedance with the SS's low input. Any rules of thumb to go by on this, like ratio's or either not to exceed?

I must admit, It sounds really damm good thru the Newcastle's pre, especially hooked to the Forte's (Many HiFi's shun them). Not harsh, great mid's. Percussion is repro'd very life-like. Sounds like there's a drum set in the living room. And the bass must have been canned and shipped in.