The RM-9 was designed before balanced was even thought of for the home. The RM-200 has true balanced inputs, not just the connector. It is easy to use the RM-200 unbalanced. It would be impractical to make the RM-9 balanced nor is there a good place to put the connector.
As long as you have no hum in your system, balanced is not necessary. In most systems balanced has no real advantage other than hum reduction due to ground loops. However, 99.9% of the time, ground loops can be easily fixed by floating all the grounds except the power amp. I have never had a situation where this did not work just as well as balanced.
