My M60s sing a hell of a lot better now with a dedicated amp. I found a discontinued Parasound model unopened in original box for a decent price on Ebay. If you're not opposed to buying used you can get some really good dedicated power. If you like it loud and have a decent sized room you can definitely benefit from a separate amplifier from you Denon.

M60|VP150|2xQS8|PSA XS30+Epik Empire|Pioneer Kuro 6010FD|PS3|Denon AVR-X4000|Parasound 5250v.2|