Under "Sound" there are no settings which appear relevant to pass-through.
While I'm in settings, however, there's a few things might be worth mentioning -
Bluetooth supports BT keyboards which operate at the same time as the Archos remote. In other words, if you suddenly need to enter a load of text, you can simply use a BT keyboard without having to do any switching/setting (once it's paired in the usual way the first time of course).
I've got poor results with BT headphones however - can't tell whether it doesn't like my particular one, or all BT headphones.
There's a setting to allow remote control from another Android device running the "Archos remote control" app which is free on the market. This provides various control schemes, eg touchpad or media control, but does not show the TV Connect screen - it assumes you are looking at the TV.
Under "Display" there's a TV overscan setting.
I haven't tried big cards so can't comment on whether bigger than 32 would work. Personally I stream almost everything so storage is not an issue. But you can easily plug in an external hard drive if you want, which is of course no issue given that the device is kept in one place. (The way it sits on top of the TV is very neat and well designed to fit practically anything).
Location services relies on wifi as there's no GPS.
Camera is not very good, and it's made worse by being shown full screen. I've yet to try it with Skype, for which it would just about be adequate I should think. On the other hand, the mic is good quality, and there is a key combo on the remote to permit voice input in most situations.
Contacts (People) app doesn't seem to sync for some reason. Calendar does work ok.
I've not seen any method of rooting online. Personally I'm fine with it as it is.
You can use it to some extent as a Chromecast device, using the "Cheapcast" app from the market. That certainly allows you to find a Youtube video on your phone, then "cast" it to the TV Connect for big screen viewing.
The most recent Rdio app update broke Rdio on this device (no player screen). I don't doubt that will be fixed in due course. Netflix works fine.
The most helpful review I've seen online is here -
That has several videos too, which should help show performance and ease of use etc.
Most of my experiences with this device can be read on http://forums.whirlpool.net.au/archive/2035173