hi, welcome to a/c!

as far as i know preamp output impedance can never be too low, only too high. you want to make sure it is at least ten times lower than the amp's input impedance.
re: balance vs unbalanced, i think unbalanced is fine, unless you have severe electrical noise issues or are running extremely long interconnect between amp & preamp. like >50'... i run 16' unbalanced ic's between my preamp and active x-over w/no issues. but, some folks thing balanced is
"it". i don't, i think there's a trade-off, as true balanced equipment requires twice the electronics inside...
doug s.