Krell KSA 200s

I do know there is supposed to be a jumper installed in the balanced inputs when you are using rca input. 
 

Whether you can leave both plugged in I’m not sure. 

You have a very cool amplifier.  Per an internet search of Krell manuals: 1) use only one input, RCA or XLR, at time, 2) if using RCA, shorting pins should be used in the XLRs if using RCA.  It also indicates that XLR is the preferred connection method.

Enjoy!

Should I just use an RCA to XLR cable and connect the preamp to the XLR input of the power amp?

disconnect the xlr from the preamp you are not useing 

or you mic get circulating current from having both connections plugged into the amp and you don;t really need the jumper for the amp.

@kunalraiker  you could but the rca is unbalanced where as the xlr is and 

and you might have problems unless you have a cable set up for this  

It really does not matter which input you use on you amp, but you cant use both,

if you only were using xlr's to both your noise floor would be better