hi again, thanks for the info. not that i understand the significance but the ats are a 42 ohm hp. the hd600s play at 300 ohms. i use a sex 2.1 with some upgrades. still considering magnequest iron. the problem is that i do not solder. i have had this sex unit worked on by shawn when he worked at bottlehead. also a good friend has installed upgraded signal wire, rca receptacles, binding posts, caps, and on and on. goldpoint switches were installed in the sex and the foreplay which serves the amp. setup sounds very fine played through my 12" audio nirvana full range speakers using cain and cain cabinets. i must confess that i did not know about a 200 hour break-in period for the hd600s was indicated. so last night i left the tv operation on a low setting with the 600s hooked up to the preamp. this will continue until the phones are indeed broken in......is it the case that sennheiser intends that this hp cable should be upgraded? i have noticed that the audio technica cable is very much more stout when compared to the cable provided with the hd 600s. so, thanks for the help, don