Hi JFM, and Welcome to Audioholics.
The 7.1-multichannel analog input, main use is for connecting a Universal DVD player for multichannel SACD and DVD Audio.
Also, for using external multichannel processors, like from a Blu-ray player, etc.
But, having all the decoders already in your A/V receiver with HDMI version 1.3, does in fact render the situation quite moot, as you can even use the HDMI single cable connection for even multichannel SACD and DVD Audio.
* Only when you have an older Universal DVD player of quite good quality and with good Dacs, the 7.1-mutichannel analog input becomes a very valuable feature. In my personal case, it is a must. I cannot live without this feature. But a lot of people now, can.
It is a personal feature that can still benefit a lot of people, including myself.
~~~ Just as an additional information; the newer Onkyo TX-SR707 has seven (7) HDMI inputs
(version 1.3 of course).
Cheers,
Bob