@OP just to clarify, the HD600/650 are of warmer sound signature slightly laid back so you may perceive the sound is little less crisp than the brighter sound signature of the K/Q701/2's. Myself and most that own the 600 or have heard the 650 prefer it for classical and jazz because sometimes that K/Q70X treble can be too bright sounding (yes I dislike it) with certain instrumentations in the piece you are listening to.
@Graphism: I actually second the SA3k recommendation here, with a good warm solid state amp such as a M3 or a good tube amp able to deliver enough @ 70ohms can sound make the S3k sound very very good. Actually I find the sound a balanced mateship of the K/Q70X with the HD600/650's. The 600 I find is more neutral than the 650 but the 650 more warmer but can scale like a behemoth depending on the amplification thrown at it.
PS: I thought the SA line was completely discontinued already?