Just picked up a used pair for cheap, 80 ohm version. Running them with my fostex portable and a classic iPod. Wow these are great.

Yes very nice with classical music!

My ears tell me the 660 offers a more detailed presentation from top to bottom. I find the 650 to have a muddy bass. The 660 has a tighter more articulate bass. This may be why some people hear the 660 as bright, due to the psychoacoustical relationship between top and bottom end.

While I won’t be putting my 6xx in storage, I agree the 660 is a better set of cans, even while listening through my microzotl2.

I really enjoy the 660s/microzotl2 combo. But I listen to vinyl primarily.

Thanks for taking the time to write this review. Is it just me or is anyone else left scratching their head after reading the inner fidelity review which purports to hear grain in the 660s?

Funny that. My HD6xx arrived in the mail and I was a/bing them with my HD 660s. I almost prefer the former with Fagen, the dan, etc. But my K7xx did much better with Radiohead than either of those.

I ordered mine directly from Sennheiser.

I had a couple of Sylvanias that got fried.

OK so I've discovered a few interesting things lately. I'm quite sure someone must have written about this before, but anyway. I've noticed the MZ2 is quite sensitive to interconnects. In fact, the only ones it seems to like in my stash are the ones made by Mr. Morin at Lounge Audio for his...

An even cheaper choice is new production EH. NEW STOCK – Electro-Harmonix EH6SN7 [PHOTO HERE] [black plates, black base, black labels on glass, top getter] ● “The Electro Harmonix were the most dynamic in the MPX3 . The Bass is also the best and biggest of the three; quite detailed and...

I've been doing a bit of tube rolling and so far the best combo for my system is the Sylvania 6SN7 GTB with the orange label Amperex 6201, probably a rebranded GE.  The JAN GE 6201 is second. The green label Sylvania 6201 sounds a bit thin to my ears, but maybe it will sound really good with the...

Apparently I got one of the last basic units made, with the 6SN7 tubes and the standard power supply. Fortunately I have on hand some slightly used GE and Sylvanias that sound very good. I did not have any 12AT7's at all, but they are not so pricey. Just received a pair of NOS GE 6201s from...

Mine are dead quiet

The MZ2 microzotl headphone amp pairs very well with the R70x! The bass is insane.