I bought a used Aragon 4004 MKII amp for $1,000 from a dealer in 1999 and used it, paired with a VTL 2.5 tube preamp, on my Magnepan 2.7qrs for over 15 years. It’s a very good class A/B amp that will deliver 400 watts/channel into the 1.6qr’s 4 ohm load. I agree with jmcgrogan2’s comments earlier, especially about the capacitors. In 2015, some caps in my amp leaked and I decided the $1,000 repair quote was too expensive.
So, I replaced it with a $630 class D audio SDS-440CS amp:
http://www.classdaudio.com/sds-series-amplifiers/sds-440cs-class-d-audio-stereo-power-amplifier/
I was pleasantly surprised that this amp significantly outperformed my older Aragon. It had a lower noise floor, more powerful and better controlled bass, better dynamic range along with a similar smooth but detailed mid-range and treble quality. It’s also much smaller and lighter while running cooler and outputting a bit more power with 440 watts/ch @ 4 ohms.
I also agree that $450 is a good price for the Aragon amp and it’s a good match for the Magnepans as long as you’re both aware it’s over 20 yrs old (I believe it came out in 1994) and the caps do have a limited lifespan.
However, for $180 more you’ll get a brand new amp with a year warranty that, based on my experience, significantly outperforms the Aragon,
A word of caution: the class D audio 440CS is very neutral and the overall sound will be mainly determined by the preamp you pair with it: ss for a neutral sound and tubed for a warmer more colored sound. But I know it drives Magnepans well and it’s a true bargain at $630.
Hope this helped,
Tim