The problem is that you cannot go by the volume position alone, especially for music listening. There are just too many variables. For example, say you sit 8 ft away, now compared with someone who sits 16 ft away in the same room, that person will have to set the volume to -24 to get the same spl you are getting sitting 8ft away. So if your amp is outputting 2W for you, it will have to output 8W for that other person. That's just one factor, with more factors involved and compounding the issue, you can see that volume -30 just don't tell us enough to answer your question. YPAO should in theory calibrate your system to provide the spl per THX standard, that is 85 dB with volume at 0, but that's THX standard, and is specific for your room, at your MIC distance. It does not tell us anything about how much power you need just going by volume at -30. We need to know the power your AVR or amp is outputting at volume -30 in order to answer you question.
The online calculator linked below has been posted many times, but for your convenience, here it is again:
http://myhometheater.homestead.com/splcalculator.html
Enter the required data and it will tell you the maximum spl you should be getting at your listening position. Then the last step is, use a Radio Shack SPL meter to find out what is the average SPL you are getting when listening to music with volume set to -30. Please realize that it depends on the kind of music, some are mastered higher than others, so you should choose the music that you typically listen at volume -30. Come back with the two numbers (the online calculated spl at your amp's rated output, and the measured spl at your listening position), the rated output of your amp, and one of us will figure out how much power your amp, or AVR are outputting. If it is well below it's rated power, say 20-30 dB below, then adding a more powerful amp will unlikely improve dynamics or details.