What should I upgrade first amp or preamp?


I need your help. I have OPPO BDP-105 connected to PASS Labs XP-10 and XA-30.5 driving 89 dB at 4 Ohm Snell C7. Looking to upgrade my system and planning to spend $ 3000-4000. I live in the apartment building and unfortunately can't listen to music very loud (no more than 58-62 on the XP-10 display).
What would you suggest to do, upgrade preamp to XP-20 first or amp to two XA-60.5 or to XA-100.5 and why. Upgrading an amp is more problematic due to the space constrains.
What will I gain and what should be the difference in sound in each of those cases?
Thank you.
karapuz
So, do you guys really think that both preamp and amp are good and sufficient enough and don't need to be changed at all? Regarding cables, I have 10" Analysis Plus Black Oval 12 speaker cables as well as 1.5 m Analysis Plus Solo Crystal interconnects. How good are they in your opinion?
Forgot to say, my speakers are tri-wired, so truly speaking I have wires that 3 times thicker than regular 12 gauge cable wires. Do you think I need something different?
That all sounds good to me, assuming that the Analysis Plus interconnects are the XLR versions. Frankly, I don't see anything that particularly stands out as a weak link, although I have little familiarity with the XP-10 preamp.

Regards,
-- Al
I know you aren't a big fan of tubes but if you were to throw a Herron VTSP-3a in there, the sound wouldn't go tube-ey. You'd just get a better sense of space and timbre without sacrificing any dynamics. I've been a high end passive guy forever and even tried some SS preamps but it wasn't until I tried a very good tube preamp that I finally got the sound I was looking for.