My Yamaha clips at 3/4 volume

The fact that it clips at 3/4 volume has nothing to do with how much power is being used.

Western,
Something doesn't add up here. Your Yamha M45 amp is rated at 180 Watts rms @ 4 ohms, into 4 ohm speakers that are efficient enough to have been successfully driven by a 10-watt rms Trends Audio T-amp! (Dingus' 2nd Agon system, Bedroom bliss with the T-Amp).

You should have way more than sufficient power to drive these speaker loads.
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Give us more details, and I'm confident one of our amazing A-gon Gurus will surely be able to help you in isolating the problem.
e.g.:
When you mention 3/4 volume, are you a) referring to the volume pot on the pre-amp, or to b)the peak power meters on the amp? If a), what peak power readings are you getting on the amp w/o failing?

Is your "Auto Class A Switch" deactivated? If not, try switching off to run in full A-B mode. (This could possibly effect handshake with pre-amp?)

What sources are you using?
Was this system ever more responsive?
What last changed?
What other components do you have to swap out for testing?

Good luck!

I'm using a Technics SL-PD867 CD player along with the amp and pre-amp. I had the volume pot on the preamp at about 2 o'clock, the left and right output levels on the amp were at 12 o'clock. I just got the M-45 and Aragon 28k, previous to this setup I was using a Yamaha A-700. I'll get it back to make a comparison.
When I checked to see if the Class A switch was activated, it wasn't. What I discovered was that both the A and B switches were both activated and the speakers are only connected to A. Could this have an effect?

Thank you Elizabeth, Rrog and Sandstone for your help.
As you can probably tell I'm somewhat of a novice when it comes to stereo equipment.

Based on your description and the fact that your preamp volume control is at 2 o'clock, I would set the M45 amp controls to fully open, and then listen again. All other posts above is great information as well.

Most amps will clip at full volume, especially when the gain on a preamp is involved. I agree with Mrdecibel on setting the amp at full volume. There are no rules out there about where a volume control should be set at.

I've owned 3 of these amps. Very good for the money. They do have a thermal protection if you are over-driving them, if I recall. Also, since you are running 4 ohms, make sure you are NOT using more than one set of speakers. Even though you can hook up more pairs, it will take you impedance way too low. I've never met a Yamaha that would handle less than 4 ohms. Are these speakers running lower than 4 ohms? You may need to have the speakers checked?

Do you get the same issues in class A and in A/B? The amp should run fairly hot in class A. Most class A amps run very hot. Enjoy it. You just got 90% of a Threshold for 25% of the cost (in my opinion).