Wemfan,
I just noticed I didn't answer your question on the remotes. As I noted before, my system is very similar to yours. I not only have the same hdtv and Oppo 105 as you, I have Directv, too. So, I'll tell you how I utilize the remotes and give you an idea of at least one way it all functions.
Basically, I use both the Directv remote and the Oppo remote. The Directv remote controls what you're viewing and the Oppo remote just controls the volume. I've found that, once you adjust the volume to your desired level on one channel, this volume works well on all channels so you can set it aside and just use the Directv remote only to switch channels. You'll only need the Oppo remote again if you want to turn the sound up, down or 'mute'.
The Oppo's volume level will be super-imposed on your tv screen when you adjust it on the Oppo remote. It's a horizontal bar that fills in as you increase volume and also displays a numeric volume readout of '0 to 100'. I set my volume in the '50-65' range for regular tv viewing and only increase to above '70' when watching favorite shows or movies.
To have your system work in the above manner, here's how to set it up: Connect an HDMI cable from the Directv 'Genie' or small 'client server' to the 'HDMI 1' input on the Oppo. Connect a 2nd HDMI cable (the 105 comes with a 6ft HDMI cable) from the Oppo's output to the Panasonic hdtv's 'HDMI 1' input. This hookup allows the satellite video signal to be processed by the 105's very good Qdeo internal video processor before being passed along to your plasma. The picture quality is excellent with this setup.
I also have a Logitech Harmony-650 universal remote that I used on my previous setup. I haven't yet felt the need to reprogram it to take over the functions of both into a single remote. This would be another option if you feel the need for it.
I hope this helped you understand how it all functions,
Tim