Avalon AUC2 converter for Avalon 6? Can I use a USB controller of sorts?
Yes, you do need an AUC to run any avalon miner.  AUC3's will work on AV6.  But AUC2's will NOT work on AV741.

I've been looking for a spare as well and have tried a few generic USB2I2C devices from china with no luck.  I'm just not that skilled with these sorts of things.