Why not just use RCAs, in any case, measurements often show you get lowest THD+N using RCAs, that's the case with both the A10 and Anthem AVM90 reviews on ASR and/or Audioholics.com
The Marantz AV 10 15.4CH 8K AV Processor excelled in bench & listening tests. With unique bass management & room correction features, it's unmatched at its price. Long-term testing confirms its AV prowess.
www.audioholics.com
av10
"At low drive level ( below 2Vrms), the unbalanced outputs exhibit slightly less distortion than the XLRs.
AVM90:
This is a review and detailed measurements of the Anthem AVM90 home theater 15.4 channel Audio/Video Processor. It was sent to me by the company and is on sale for US $6375. As you see, the AVM90 sports a gorgeous, high contrast and large display. It is a joy to navigate this feature as it is...
www.audiosciencereview.com
"That is already good performance but we actually get more by switching to RCA out:"
If you have to use long interconnects, such as 4 meters, XLR may be of clear benefit in terms of minimizing common mode noise, otherwise unbalanced/RCAs are just as good, sometime even better.
XLR offers better connections imo, but there really is no gain in terms of sound quality, unless again, you get into noise such as ground loop noise.
The A21 and Outlaw 2220 both have good gain, so there is no advantage to use XLR that offers 2X the voltage.
If you must use XLRs, I would still avoid the 7776, may be take a look of the AVM70.