i like tube buffers. it is absolutely mandatory, imo, for use between my new sony xdr f1-hd tuna & (tube) preamp. makes a big difference. makes tiny but still worthwhile improvements between other s/s tunas & preamp, & between dac & preamp. i also use one between the hi-pass output of my deqx & a tube amp. i dunno if it makes an improvement here, cuz i never tried running the deqx w/o it. but, as the deqx is a s/s digital dsp dewice, it yust seemed like the right thing to do.

tube buffers i use are ase z-man, w/exception of a kailin mu-1, which is between dac & preamp. z-man is discontinued, but shows up used every once in a while. i dunno what's happened to kailin; i don't see any of their stuff f/s any more... i would awoid a used musical fidelity x-10d - i have heard one, & i think it's a bit coloured, the ones i use i think are completely neutral sounding.
i have tried a z-man between a s/s preamp & both tube & s/s amps, & it was a tiny improvement, imo.
i would not spend a lot of money on one - i do not think the cost/benefit ratio is there. these are not substitutes for quality tube amp & tube preamp, imo. check ebay for yaqin tube buffer. search title, description, & check the "worldwide" option. careful shopping & sniping will nab you one for <$150. for that price, it may be a worthwhile tweak for your s/s system.
doug s.