I've got HD580's myself, so I don't know by experience about the optimal feeding of the HD650's. There are a lot of comments from HD650 fans about looking to optimize the high end of their sound, as the low end of the 650's is so full and solid. I've got a high bias M^3 with AD843's, STEPS and Blackgates built for me by Rockhopper Audio. In addition to the full, very slightly warm, prominent mids sound that the M^3 has come to be known for, I'm getting the most beautiful highs and sonic imaging I would know how to ask for. Since I got the M^3 a few months ago, I've been using the AD843's that I ordered for it. In a month or so, when I'm sure that it has fully settled into its optimal sound, I'm going to try it with a set of OPA627's to see how that compares. With a PPA fitted with the Larocco Discrete Buffer, the OPA627's were my hands-down favorite opamp over the AD8610's or AD8065's. I'm interested in hearing how the 627's compare to the 843's in the M^3. But, with the 843's, STEPS and Blackgates, the M^3 is delivering a gorgeous, no-veil, high end through the HD580's with better and more subtle, refined, fully-formed low level detail than I ever got from the PPA, along with its often-described signature sound. I'm finding the M^3 to be a worthwhile upgrade from the PPA, mainly in terms of the everyday music listening pleasures that it delivers. I've not yet had the pleasure of hearing a Woo3 (sigh) - maybe someday.
