i just got my hands on an ampeg svt1000 bass head. i want to record from the line out on the back of it. it has a balanced (xlr female) and an unbalanced (1/4") plug on it. which should i use and why? when i follow this signal chain, (xlr female to balanced 1/4" cable into my stage box's send/return jack in my live room, into my la610's line-in in my control room) i get a buzzing sound howcome?