Purchased a pair of the 450M Mono blocks in March of 2011.
Did the 900+ hour burn in as required.
It will depend on the rest of your system. Speakers and head end equipment.
This is only from my point of view. I own Audio Research Ref 5 Preamp, REF 2 Phono preamp, and CD-5 CD player. Have owned most of Audio Research Equipment. Speakers are Acoustat 3M's, Full range Electrostatic. Main listening is Vinyl. After the burn in period compared the Audio Research 450M'a to my Acoustat TNT200 power amps.
[However I should explain that these are no ordinary TNT Power amps. Roy Esposito, a former Electrical Engineer for Acoustat, updated these power amps, added balanced inputs and converted them to Mono Block power amps with approximately 1KW of power output.]
After serious listening comparing both amplifiers I chose the Acoustat TNT200 units over the Audio Research DS450M.
The 450's did not sound bad. They are a very fast and great sound amplifier. However, the TNT200's just sounded better to me. Sonically I would say the Acoustat Amps are smoother, especially in the upper mid range and top end. One other thing. The Audio Research 450's
do not get hot, no matter how hard you drive them.
Sold the 450M Mono Block power amps.
This is only my experience. Different Head end equipment and speakers may have given end results.
Hope is helps.