Agree that NC122MP and PA5 are roughly even on power output and I would consider both rather power limited. As far as I can tell the NC122MP is not very popular and I imagine power output (for the price) is a primary reason. Agree that PA5 will outperform NC122MP in terms of noise but I imagine NC122MP has less frequency response variability in to complex loads and has better higher frequency distortion performance than the PA5. I am sure that both sound great when used within their power limits.
Personally I would opt for a NC252MP over either as it is not that much more expensive, I like to have more power on tap, I run DIY active speakers so having an adjustable volume knob is a liability, prefer an in-chassis power supply and I know it will give me excellent system noise performance as I long as I use a reasonably low noise DAC (>108 dB DR at 2 V).
Michael
My reasoning would be similar, though PA5 may have a bit better 1kHz THD+N, at higher frequencies is NC122MP better, it will be more load invariant including complex load, better in HF intermodulation CCIF test, and it keeps lower distortion up to higher power than PA5, the usable power is higher.
and I prefer mechanical design of the Audiophonics MPA-S125NC for these reasons:
1) bigger speaker binding posts. Small binding posts of AIYIMA A07, Topping PA03 and PA5 make it difficult to use with thicker speaker wires or latching banana plugs. I myself cannot use the A07 in my main system without using an adapter for speaker cables (in fact additional binding posts with a piece of wire), because the distance of speaker terminals of the A07 is too small.
2) I prefer XLR connectors to 6.3 mm TRS. Though both are reliable, the XLRs are safer for a simple reason - TRS when unplugged at one side leaves the Tip (T) pin, which is connected to +live signal exposed to random contact with metal cases in the vicinity and there may be a static discharge or voltage difference that may destroy output of the connected DAC or preamp. These have almost never an overvoltage or ESD protection. Such scenario cannot happen with XLR connectors as their pins are covered. And, the XLR always connects pin 1 (ground) first, which is also important. All in all, XLRs are safer for use than TRS. TRS are rather good for PA systems that have usually better protection of input and output circuits than the consumer audio.
3) Built in power supply with standard IEC mains plug is a big advantage of NC122MP/MPA-S125NC.
I can see no technical reason why I should prefer the Topping PA5 over MPA-S125NC.