What should I upgrade first amp or preamp?

JL, as the average volume level is reduced, the volume of dynamic peaks will be reduced by the same number of db. Per the calculation methodology I described in the thread you are probably referring to, with the OP's speakers listened to at a 3 meter distance the XA30.5 wouldn't leave class A until levels of around 97 db were exceeded. (It's coincidental that the 97 db figure in this case is the same as in the situation in the other thread).

I doubt that 97 db would be exceeded on dynamic peaks more than rarely (if ever) in the circumstances the OP describes.

Best regards,
-- Al

There are several upgrades you could do...

Try a Pass X150.5. I was told that although the XA sounds warm, the X.5 series has better bass control, better detail, better clarity, faster speed and better articulation for dialogue in movies. Cost approx $3900.

Try Grover Huffman cables. They are endorsed by Steve Hoffman, famous studio mastering engineer. Grover only offers one quality level, his best, no hype about spending more money to get better sound. His design is patented, he has over 10 years experience, offers a 60 day money back guarantee. I have never seen a negative about them. A reviewer from Positive Feedback wrote " Well, for circa $1000, you can connect your entire system with Grover Huffman cables, and you will be hard-pressed to find better. Each of these items—interconnects, power cords and speaker cables—is in the first rank of its respective class, and has my highest recommendation. Truly outstanding. Tom Campbell" Affordable Audio wrote "Grover Huffman cables are the most affordable cables I've had in my system for years, and yet in many ways they are the best. Regardless of price, their strengths lie in the musical balance and timbrel accuracy they bring to the fore, assuming your system can provide these. These are qualities that really matter for me, but the Huffman cables do this without any loss of detail or curtailing of frequency extremes. You can pay more, you can pay less, but if there is a sweet spot where sonics meet cost, Grover Huffman is sitting in it. Highly recommended." $230 for 1meter XLR pair. Speaker cables $20/ft.

Try a different preamp. Classe SSP600 can be bought used for $2000 and Meridian have good reviews. For even less money but more features you can buy an Integra DHC-80.2 with Audyssey room correction, equalizer, internet radio, and FM and HD radio. Kal Robinson, editor of Stereophile uses one.

Modwright Oppo blu-ray players are great. I lucky to find a used BDP-83SE. You could buy a BDP-95 for $1k and do the stereo mod for $500. The benefits are described as "The end result is a clear improvement over the stock player, ridding the music of digital edge and glare and providing a significant improvement in overall musicality. The lower noise floor and cleaner signal path allow for a broader soundstage and greater refinement of overall resolution and detail. This is due largely to ridding the circuit of one entire op-amp stage, as well as upgrading the signal path resistors and improving the remaining op-amp stage."

Karapuz,
Here is a different idea: If you live anywhere near Atlanta, you can spend a fraction of your budget and hire Jim Smith to voice your system. He can come over to listen and on the rare chance that he does not think a voicing session will improve your sound, he will not charge you his fee. I now have heard three systems that he has voiced, and the results have each been outstanding.
If you don't live near Atlanta, get his book or DVD and work on this yourself. You will be surprised at the level of improvement a well-voiced system will reach.
I know that does not answer your question about amp or preamp upgrades. It would be helpful to those trying to offer you advice if you describe what you think your system is lacking.

You may also want to check other threads for speakers that excel at low volume. While the C7's are certainly worthy of your system, they might not be the best low volume choice...

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.