You didn’t say how you were monitoring the audio. A common issue with Kona 3 cards is audio popping if ref video is not fed to the card. The mix of audio file sample rates could be related as FCP is doing the sample rate conversion on the fly. Have you rendered the audio tracks?
As for going back to FCP 6, if you have important work to get out, do so. Hopefully, you cloned your drive so that’d be easy.
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.8 QT7.6.4 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24″ TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
FCS 3 (FCP 7.0.1, Motion 4.0.1, Comp 3.5.1, DVDSP 4.2.2, Color 1.5.1)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN