The major difference between the two amps is that the 7200 has only unbalanced (RCA) inputs. The 7700 has both unbalanced and balanced (XLR) input connections. The input type on the 7700 (and 7500) may be selected per channel, running a mix of RCA and XLR cables as required. Balanced cable design offers superior immunity to noise/hum pickup in the cabling and/or due to ground loop interactions.