"why is there a significant market for USB clean up and reclocking devices by Uptone, Intona,IFi, Schiit, Berkeley Alpha, InnuOs, Aqua, DCS et al?Are they all selling snake oil?"
I cannot say what others are hearing (or think they are hearing) by adding these devices. I’ve added a couple (from Uptone, Sonore/SGC). When the devices do recognize each other, the SQ is quite good. However, it isn’t necessarily better than the SQ I get from ethernet or S/PDIF. It’s just that I can’t help myself from tinkering with HQPlayer filters and such through USB. For most "normal" people (not OCD audiophiles) this would be a complete non-starter. They do not have the skills/mind-set/patience to go through the trouble-shooting needed to fix a broken USB handshake. Just plug in the ethernet or S/PDIF cable, enjoy the music, and be done. Caveat: I own pretty good (but not phenomenal) gear and am in my 60s. Maybe with better gear and ears, I'd notice bigger SQ differences.
I cannot say what others are hearing (or think they are hearing) by adding these devices. I’ve added a couple (from Uptone, Sonore/SGC). When the devices do recognize each other, the SQ is quite good. However, it isn’t necessarily better than the SQ I get from ethernet or S/PDIF. It’s just that I can’t help myself from tinkering with HQPlayer filters and such through USB. For most "normal" people (not OCD audiophiles) this would be a complete non-starter. They do not have the skills/mind-set/patience to go through the trouble-shooting needed to fix a broken USB handshake. Just plug in the ethernet or S/PDIF cable, enjoy the music, and be done. Caveat: I own pretty good (but not phenomenal) gear and am in my 60s. Maybe with better gear and ears, I'd notice bigger SQ differences.