I think if anything you're going to need something to boost the signal, not lower it. The rca's on the ua5 are expecting a line-level signal and unless the c1000s put out a really hot signal you'll need either a preamp or some line transformers (like AT8201s) to get a signal that's similar in levels to the XLRs on the front. It's been mentioned here a bunch of times that the knob on the back is an atteunator and doesn't add gain, but rather it reduces gain. If you do end up using some AT8201's you'll still need a way to go from the male 1/4" jack on the end of the 8201 to an RCA connector. I ended up getting some female 1/4" to male RCA adapters along w/ some short male RCA to female RCA cables that plugged into the ua5. You could do it without the cables and plug the 8201 w/ adapter directly into the ua5 but it'll be sticking straight out of the rca jacks about 4 inches.