Both very good choices OP and like the comment above I would surely be happy with either. I use the 509x and always remember this quote from a review of it:
For argument and sake of reference point, if you were to put Boulder amplifiers (and we still had the 1100 series here for comparison) as straight-up natural at 12 o’clock – adding nor subtracting nothing, with no sense of added tonal saturation, our reference Pass XS Pre/XA 200.8 is probably at about 10:30. With going to the left a bit on the warm/saturated side. The Luxman 900 series was about 11:30, with our tube references the PrimaLuna EVO 400 and VAC i170 coming in at about 9:00 and 9:30. I’d put the recent Esoteric integrated about 12:30 – slightly to the cold side, and the last few Simaudio amplifiers we’ve reviewed about 1:00 – even more clinical. The L-509x, like it’s larger separates has that same touch of warmth/saturation, without being slow or non-resolving. I wish I would have had the ability to listen to them both side-by-side and suspect that the L-509x comes very, very close to the 900 series in terms of sonic performance.
The 11:30 reference point spoke to me. Further Luxman supports HT bypass and at the time Pass didn’t, so easy one for me. Good luck, can’t go too wrong.