Is Sony XA-5400ES fully 'truly' balanced?

Just purchased new Sony XA-5400ES SACD player. Sounds fantastic after a couple hundred hours. Currently running 'inexpensive' Kimber Hero SE interconnects. Was wondering if any benefit should/would be realized from changing to XLR balanced cables? Not sure if the Sony is a fully balanced unit? The preamp IS fully balanced Krell KCT.
You don't have any XLR cables to try for yourself? If the Sony is fully balanced then yes you will hear a significant improvement. I have a fully balanced cdp, Cary 306 Pro, going into a VTL 6.5 preamp, also fully balanced, and the difference was like 50% better w/ XLR.
No. I haven't had a source with XLR outputs in years. As I recall the last time was with the SCD-1 and I believe that WAS fully balanced. Not 100% on that either.
It has a balanced output and it's done correctly. The SCD-1 was not done correctly.

I have mine connected to a BAT VK-50SE preamp - it only allows XLRs, and of course, is differentially balanced. I hope you can try connecting the balanced outputs of your 5400 to your preamp. I'd like to know if you perceive a difference.

I've had a Sony xa-5400es for 7 months now and ran Audioquest King Cobra RCAs for a couple of months then switched to King Cobra XLRs and it made a noticable difference in sound through my McIntosh MA6900 and PSB Synchrony Ones. It is interesting that the system plays louder through the RCAs but sounds smoother with the XLRs.