If they were both the same MSRP, it would be a toss up because they would sound the same and have similar features & power. But in this case, I would pick the flagship model Z9 all the way. The Samsung BD-UP5000 can internally decode & send TrueHD, DTS-MA, & PCM to the Z9's analog inputs so you would not miss a beat.
If you ask if I would pick the Denon 5805 ($7K MSRP) or the Z9 ($4K MSRP), I would pick the Denon 5805.
You might want to check out the Onkyo SR875 too:
http://www.amazon.com/exec/obidos/ASIN/B000OBLARW/interactiveda8704-20