[linux-audio-user] different sound cards drift problem with spdif

I have two audio cards: (integrated) 00:11.5 Multimedia audio controller: VIA Technologies, Inc. VT8233/A/8235/8237 AC97 Audio Controller (rev 50) using driver: snd_via82xx (PCI) 00:0c.0 Multimedia audio controller: Creative Labs SB Live! EMU10k1 (rev 07) using driver: snd_emu10k1 I connected the two with a spdif connector because the internal one seems to have a better ADC than emu10k1 (Sblive external Digital Out jack to Internal Spdif IN) When I play any file on the sblive, and ONLY if I listen it on the other card, I hear a click every 3 seconds. If I listen to the file directly from sblice line out it's OK. Maybe it's because of drift (of ~3hz) of the two card spdif clock. How can I make the two card sync'ed?