You don't give a price range for cheap, so I will share my thoughts in general.
In truly budget amps, I personally think NAD is really tough to beat. I have had Marantz, Rotel, Adcom, Carver, HK and others. NAD is more musical and a great value. I don't care for Rotel or Adcom as both are to hard and transistor sounding for my taste. I had your AV550 paired with both Adcom and Rotel in the past and did not care for the combination.
One issue with older monitor series NAD amps (like the 2400) is the relay switches dry out. I have both a 2100 and a 2400 in different systems and they cut out at lower volume levels. You simply need to turn it up and then back down. Not a big deal, but can be annoying. For me, NAD gets the essence of the music correct, the tonal balance. What they don't give compared to expensive amps is soundstage, seeing into the music, nuances etc. Of course that is generally much more money to obtain.
That said, if you can spend more, like $5-600, I think the Musical Fidelity A3 is an absolute steal on the used market. Clear, tonally accurate, built like a tank. Compact and beautiful. This is an amp you could keep for some time and not have your system outclass it.
Drop me a note if you wish to discuss further. I have a few amps not being used and could let one go cheap if you are interested.
Of course, all of this information needs to be taken for what it is. My opinion only. Your taste, room, system etc all contibute to what is the right choice for you. Some like Bud, some Miller and some Coors. Some can't stand any of them. Who is right? Who cares.
Enjoy the music
Regards,
Paul
