I have a Vizio 5.1 soundbar, with no HDMI input and use optical from it to the TV. My VIP 612 passes dolby digital to it. At one time TV's did not pass 5.1 over optical from the HDMI sources but that has changed. My LG TV about 2 years old and my Samsung TV new both will pass 5.1 over optical.
Are you sure the programming you are watching is in 5.1 on the 722? Very little daytime programming is, not many OTA sub channels are even much other programming is not. When you are watching on the Roku is 5.1 always indicated or only for programs that really are? One other thing, I do think sometimes ARC will not pass it. You might try a different HDMI cable from the 722 to the TV, especially the one the Roku is using since you feel that is passing 5.1.