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
I agree with Ejlif. A new preamp would be a better choice over a new amp. Looking at your system, though, I think your weakest component is the Oppo. Both your amp and preamp are 0 feedback, fully balanced designs. Take advantage of those features by getting a source that is a better match for them. The first player that comes to mind is an Ayre C5. It should play all the audio formats your Oppo does and is a much better match to your current system. There are other good players, as well, but that would be my 1st choice.
I agree with Zd. Another option would be to send your Oppo to ModWright. I think you will be very pleased with what comes back.
Thank you for your responds. I looked at ModWrite ipgrades befoere, however I'm not a big fan of tubes and prefer SS in all chains.
Why not upgrade power cords and add power conditioner which will be far cheaper than adding new component.