Balanced to RCA

+1 re. "You need an adapter"

I had to do this for my fully balanced Preamp to SE SET amp.

You will have to ground one of the pins. Important because it is protective. Find out which one, based on your output component (XLR side)?

I went with Cardas. They offer two levels of XLR to RCA adaptors. When compared directly, I found easily heard differences in sound between the two.

Cardas will custom spec their adaptor, if your ground needs require something different than their standard/stock offering.

I defer to @gdnrbob on the transformer approach as I chose not to go that route. Reach out to Bob for more on that and whether it will be superior to adaptors for your application.

@almarg  and @mike_in_nc   Thanks!

@mike_in_nc   I'm unsure regarding your comment below. Can you elaborate?

I was very concerned about this very issue and a number of folks helped me out. Al ( @almarg ) was a primary advisor on this. Perhaps he can comment and add his usual dose of clarity to the discussion?

I also reached out to the designer and manufacturer of both the Preamp and Amp. Both verified that the approach @almarg and others recommended was safe. I also verified with Richard Gray who is local to me, before moving forward. 

Thanks.

Adapters from unbal to bal sometimes ground one of the active pins (2 or 3 of XLR), but that is not advisable going from bal to unbal, as you would be grounding one output of your source component, which could damage it.