My current opinion...However, it is bound to change soon...I put an order for a JVC FX700 and a Sony XB90EX.
IE80 = JVC FXZ200 > Westone 3 > Westone UM3X = CKS1000 > Denon C300 > Atrio M5 (MG7)
I received my S500 along with the JVC FXZ200s and ATH-CKS1000s. I must say the S500 sounds great. Very clear and clean. Also a light weight headphone that is portable. I am more of an IEM guy, but this headphone is coming out with me....
My experiences with Tenso is great. I received three packages from them. Buy from Amazon Japan, and ship to Tenso. It took less than a week for my new, less expensive packages to arrive to the NYC area.
I picked up a pair of these. I wasn't totally impressed. The sound wasn't what I thought it would be. The build of the IEMs were shotty to me. I wasn't a fan coming from better built and sounding in-ears. I could see the sound...