What should I upgrade first amp or preamp?

Thank you all for the answers. I really appreciate your help and advices. However, I still can't decide what to do. It's so difficult, especially if there are so many choices. Yes, XA-100.5 is much more expensive than 30.5 and I'll need to spend twice as much. At the same time almost everybody are saying that stepping up from 30.5 to 60.5 in my situation doesn't really make sense because differences are not going to be huge and step up should be to 100.5 to hear the real difference in details, soundstage, etc.
Should I change the preamp to XP-20? Will I see a huge difference? I don't know.
With OPPO I like its capability to play DSD from my hard drive and DAC in it is pretty good.
I'm not changing speaker wires and interconnects, as well as my speakers, I think they are also good.
So what should I do!!!??? :) Any other suggestions would be appreciated.
i guess, first I'll get the SPL meter and check the loudness of my system at the sweet spot and continue from there.
Thank you again.

All your stuff is very good, and there is no right answer, just your personal preferences. I have had the XP-20 for a few months and it is awesome. Can't go wrong with that upgrade.

I’m also thinking the XP-20 due to the much larger power supply. I say this from experience with another Nelson Pass preamp, the Threshold FET10. I owned the original, then added the larger upgraded “e” power supply, and then upgraded to the FET10e. The power supply upgrade was the most significant step up in overall performance between the two changes.

Call Mark at Reno Hifi, he can describe the differences in all the Pass components.

OK, I measured the volume of my usual listenings and got the following numbers: I sit about 6-7 ft from my speakers, average volume is 75-80 dB with 80-90 dB in peaks, max average volume (never got louder yet, but may try this weekend) is 80-85 dB with 95-101 dB in peaks. Most of the time the meter stays around 12 or moves for a second to 1 pm during peaks. Never stays over 12 for more than two sec.
Please help me to understand those numbers, how good (or bad) and efficient my system is and whether my amp is sufficient enough or I need to move up to the next level.
Thank you.