I'm sure you already know this, but you are aware that you could go direct to the line-in on the 660...assuming yours isn't an Oade ACM modded box. Stock of course has the line-in and the busman modded 660s also leave the line-in intact. I'd imagine the reason you're asking is that XLRs lock-in and are just better connectors that a 1/8 stereo mini plug, so I don't blame you for wanting to use the XLRs. However, you need to remember though that the XLRs route through the 660's preamps without the option to bypass the preamp. The only option to bypass the 660 preamps is by using line-in. So, I'm not so sure you'd be getting the cleanest signal going from your battery box through the XLRs. This would be especially true if it's a stock 660 with electronics that I've heard aren't all that clean (the one I owned was modded by Busman, so I can't comment on stock preamp performance).