HDMI or 7.1 out for best AQ

I recently purchased an Oppo BDP-83 universal player that I will be getting modded in the near future. Some of the mods out there are pretty specific as to what is upgraded in the player, i.e., 2-ch vs Mch vs HDMI outputs. My question to you folks in the know is this: what is the best type of connection to use between the player on HT processor, separate 7.1 RCA's or HDMI? By having an answer to this, I will hopefully know where to put my money most wisely. TIA.

Bill