Amp/Preamp Synergy for 6K Used

Back to solid state? :)

Seriously, I'd look first at a Foundation Research V6 tubed preamp for about $4k new and then a solid state pair of mono Odyssey Stratos amps at $1k each. That's about as far as I'd go the tube route in that budget range.

Assuming, the synergy is there, it could be an excellent sound.

-IMO

I'd go with a Supratek Syrah preamp and a Berning ZH270 amp. That gives you a super phono stage which can handle just about any low output MC cartridge, from .2mv and up, and beautiful 6SN7 based line stage. Couple that with the speed and transparency, and power of the Berning ZOTL circuit. A strong 70 watts, with no "tubey" bloat or rolloff. A full function, crystal clear, strong powered, full frequency extension system. Sorry, no remote. The Berning used might be had for $3500, and the Syrah has a waiting period and is $2500 new, with no used units around. That pushes the $6k to the limit. But it would be tough to beat. You don't really need that remote anyway, do you?

I have a VAC standard LE preamp running into Quicksilver V4 amps (120w)and they work very well together. You can find the VAC for ~$2k w/o phono and the Quicksilver V4's for ~$2.3k.
I think the phono section from VAC is an additional $500-$1k.
I picked up the Quicksilver V4's new for $3k. If your interested I can give you the dealer name.
VAC & Quicksilver are both build solid reliable equipment.

IMHO synergy between amp and your speakers of choice is more important. I would start with Speaker – Amp pair and then selected preamp and front end.
Generally speaking I would stay with products of the same manufacturer. I lived with BAT Vk-5i + Vk-60 + Vk-P5(phonostage) for a while. Works very well with moderate to high sensitivity speakers. Could be had for slightly over $5000. You will have some money left for tube upgrade, interconnects etc.