If you want to use the balanced out, you can purchase a XLR to RCA cable, and it should be fine, but you might want to just use one of the two RCA sub outs. There probably won't be much of a difference, the balanced outs are mostly to help with keeping the signal clean on long cable runs. Funny, I just purchased a SVS ultra passive sub, and had a hard time finding a short XLR to RCA cable to connect the sub out to my amp. Ended up finding one, but until I saw your question, was thinking the 990 did not have a balanced sub out. Not sure how I missed it, especially since it's location makes it the most visible of ALL the outs on the back of the 990....my amps only have balanced inputs, so I use the balance outs for all the other channels, and must have saw the SW balanced out when connecting up the others, but just forgot about it. Now I might end up taking the XLR to rca cable back, and getting a regular XLR to XLR cable for the sub.