Giga Multiroom? Never tried it
I have always used either Fallback server or now Client Server mode in OpenViX.
Currently I have both my Xtrends in C/S mode running off the GigaBlue which works for me.
The App GigaBlue Player? Currently needs updating as the current version does not support the 4K, I use Vu+ Player
With the FBC tuner, I can easily support streams to both Xtrends, the Vu+player and watch/record something