What should I upgrade first amp or preamp?

the other option is a new DAC to run your oppo to your pre.
You may also be able to add a couple of power cords and stay in budget.

I agree with the first couple of posts that changing the XA30.5 to either of the Pass monoblock models is not the path to follow. For one thing, given your relatively low listening volumes you are undoubtedly almost never driving the XA30.5 out of its class A operating region, much less approaching its class AB power limits.

Although perhaps the most significant improvement that would be realized by going to one of the monoblock models would be that they would allow you to use shorter speaker cables. But chances are that could be addressed more cost effectively by upgrading the cables themselves, or by paralleling a second run of the cables you are presently using. The relatively low impedance of your speakers (4 ohms nominal, 2.3 ohms minimum) makes speaker cabling a more significant consideration than would otherwise be the case, and even more so if your run lengths are longer than average.

Regarding the source component, Zd's recommendations are always extremely knowledgeable, but fwiw I would point out that according to the description of the BDP-105 at the Oppo website "the balanced output features a true differential signal path all the way from the DAC to the 3-pin XLR connector."

Regarding power cord upgrades, fwiw I recall several posts that have been made in the past by members I consider to be credible to the effect that Pass class A amps seem to be less sensitive to power cord differences than most other amps of comparable quality. Given the low impedance of your speakers, my instinct would be to focus on speaker cables before power cords, to a greater or lesser extent depending on their length.

Regards,
-- Al

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