Keep in mind really-really good 6SN7 tubes are becoming harder to find, just went through this past few years trying several new, multiple NOS collections, adding a few more NOS. Then, bought some boutique 6SN7s no longer made. If you do go with a 6SN7 based preamp, and must buy new tubes, try the Sophia Electric Blue - not cheap but nice.
Looking around you see a bit of a paradigm shift by some preamp and amp designers now leaning back to 12AU7, 12AT7s for better tube availability.
re: SLP-98*, while It’s well above your price point for a new one, keep any eye out for a good used one. A good friend who bought my prior tube amplifier also demo’d the XA-25 with is SLP-98 and liked it a lot. Has an outboard transformer and decent volume control for a remote preamp. Also, has two sets of pre-outs, kinda rare.
I spoke with Nelson a year ago and he told me personally that he has several customers running the SLP-98 with his XA amps, fwiw. I won’t give up my 6SN7 based preamp for a long time, but I’ve managed to hoard away multiple quads of NOS and new boutique 6SN7s as backup just in case - the majority of the new re-issue and new limited production 6SN7s just did not cut it for me. Your results may vary...