Looking to upgrade my preamp, suggestions?

I like my LS-25 Mk II - you might listen to an Ayre

I have been enjoying my Modwright LS36.5. Well designed preamp with isolated tube rectified power supply and a pair of 6H30's in signal output stage. 

Yeah lots of ARC used options in your price range would no doubt be good options. One other that has recently piqued my interest is Linear Tube Audio. They now have a remote version of their preamp at half your price range new, and I think they offer in-home trials that would be great at least for perspective if nothing else. Another good option would be VAC, but they’re pretty tough to find used in your price range.

I’d hesitate to recommend a solid state pre. I just think you’re used to the tubed sound, and although there are certainly some great solid state pres out there that may indeed help in the bass area there may be other trade-offs that might not be worth it. Plus there are so many great tubed options out there. FWIW and best of luck.

If you want used, my BAT VK51SE originally sold for $9k, but I see them go for just about your $3500 budget. It would have nice synergy w/your amp. I've considered replacing it a couple of times and just couldn't find anything that suited me more without spending a boatload. The solid metal remote, mono switch, polarity switch, programmable name display, and programmable volume for each input all combine to make it very convenient. I always like to think of myself as someone who won't sacrifice sound quality for convenience, but I must admit these features are useful and nice to have.
If buying new, I strongly suggest checking out Backert Labs preamps. They sound amazing, are a tube roller's dream and offer great value. If I ever make a change, that's the first brand I will consider. Cheers,
Spencer