syncing issues with class compliant hardware (01V96i...)

[Blindekinder]

Hi!
I'm experiencing issues when using some class compliant hardware:
-01V96i: many clicks (every 10-20seconds)
-Astell&Kern SR15 (portable hiQ player, usb mode): periodically (~5 min.) makes a fading-in-digital-artifact-noise and a small click at the end, like if it has to resync

they both worked OOTB . These issue are not related to xruns in jackd, although there are some with 01V.
With other stuffs I have no problem (RME multiface+expresscard HDSP, A&K AK70, focusrite, Edirol FA-101 firewire, tascam console, sonosax M2D2...)

I'm looking for a setting to fix that, without sucess...