What actually determines volume power? Is it watts?

Cl a ss d amps like d sonic pascal ant vtv ncore can put > 2000 watts into 4 ohms and sound much better that previous versions.there around 2k$.a fosi audio mono with 48 volt gan power supply from fosi is about 200$ and puts out 300 watts mono block. Most have 30 day trial. Power or watts is energy times amps that's the equasion.class d amps are light 80% efficient due to design. Marantz mcintosh denon ect are now all making class d amps. Might be worth a try for you.does your yamaha have a pre out if so use it as your pre amp.enjoy the musicand the search.

I have run into the same issue with my set-up.  I have a Parasound A21 amp that is rated at 250 watts at 8 ohms and 400 watts at 4 ohms.  My speakers are Martin Logan 60 XL, rated at 4 ohms and 92 sensitivity — so should be easily handled by my amp,  But I seem to run out of steam too at the higher volume levels.  On Reddit, a guy told me that amperage is more important than watts when it comes to volume.  He looked up stats for my amp and said his smaller amp had higher amperage and that is why he never ran out of volume on his rig.  I don’t know about these things, but I just assumed that a high wattage amp would be equipped to drive high sensitivity speakers to anything I could want.  

I have run into the same issue with my set-up.  I have a Parasound A21 amp that is rated at 250 watts at 8 ohms and 400 watts at 4 ohms.  My speakers are Martin Logan 60 XL, rated at 4 ohms and 92 sensitivity — so should be easily handled by my amp,  But I seem to run out of steam too at the higher volume levels.  On Reddit, a guy told me that amperage is more important than watts when it comes to volume.  He looked up stats for my amp and said his smaller amp had higher amperage and that is why he never ran out of volume on his rig.  I don’t know about these things, but I just assumed that a high wattage amp would be equipped to drive high sensitivity speakers to anything I could want.  

Here's an opposite story.  I have an old Krell stereo amplifier, pure class A, the KSA80.  It is rated at a mere 80-Watts per channel into an 8-Ohm load.  It is a big beast, I struggle to pick it up, and it has been rated as one of the 10 most influential amplifier designs of all time.

But it is also rated at 160-Watts per channel into 4-Ohms, and 320-Watts into 2-Ohms.  Each time the load halves its impedance, the amp delivers twice the current, and Watts is current times voltage drop.

I now use it with KEF Reference 1 speakers.  These have a sensitivity of 85-dB for a 2.83V signal at 1-metre distance, so quite low efficiency.  Nominally 4-Ohm speakers, they drop to 3.2-Ohms.  I have NEVER hit my personal volume limit and I play music loud.

Pushing the lowest bass out to a powered subwoofer obviously relieves the main amp.  I have a class D subwoofer rated at 1250-Watts RMS, or 3000-Watts peak power.  It has an input level selector and I run it on level 3 out of 60.

When looking at amplifier specifications, they tell almost none of the real story.  Look at the amount of distortion they claim at the rated power. Is the rated power with just one channel driven? How much does it drop when another channel is driven?  Droop here tells you the power supply cannot keep up.

Is the power given into 8-Ohms, or maybe 6 or 4-Ohms?  If it is for 4-Ohms, expect it to be only half that at 8-Ohms!  Does the power double each time the load impedance halves?

Almost all speakers have nasty dips in their impedance in crossover regions.  There is no such thing as a speaker that is 8-Ohms right through its frequency range.

If your speakers don't play loud enough, you could try sitting closer ... and I could keep banging on, but I won't.

My guess is that this amplifier is thinning out at high volumes and can’t keep up with the demands of the music and the speakers. A high current amp of the same wattage would probably sound fuller at high volumes and might scratch the itch. I would look for a 150-200 watt minimum amp that doubles its wattage from 8 to 4 ohms, and is stable into 2 ohms. Coda, Pass, Krell etc.