How to upgrade from Aragon 4004 mkII amp

Unless you have a few grand to spend for a small improvement I'd just keep the Aragon. That's a good amp. Heard one through some VMPS RM 40's and it worked excellently through these extremely revealing speakers. Upgrade your dac or try a tube preamp for a more significant improvement. The amp is very good.

I have an old school (Mondial) Aragon 8008 and wouldn't trade it for anything else. It feeds a pair of B&W CDM9-NT's and they absolutely sing.

Keep it!

I owned the 4004 MkII and moved up to the Classe 300, then the Mark Levinson 335 and eventually to the 336. There was a definite improvement with each upgrade and I don't regret selling the Aragon at all. The other amps, especially the Levinson, allowed the speakers to really shine in every area of sound reproduction. The Aragon is an excellent amp but depending on your source components and speakers you should find an improvement with higher end amps.

I had one for a while as well, and went to an Active Linn system (3x5105's w/5140's) and never looked back. The 4004 Mk II is a solid amp, but the linn stuff is so much smoother in the upper mids and highs. I lost all the graininess I heard with the Aragon when I upgraded, the bass changed slightly, somewhat less punch, but again, this area also became more natural with the Linn system.

FWIW my old 4004 is still in the family, it powers the woofers of my brothers ML Monoliths III's. It's up to you if you keep it or not, but I personally am very happy I did upgrade.