That's strange:confused: I would have thought that would work since the audio would stop at the Onkyo. Do you have HDMI Audio off? I'm not sure that's the name of the setting but it's to let the Onkyo know that HDMI audio is not going to the TV.
Thanks for the suggestion - I checked and the HDMI Audio on the Onkyo is already set to 'off'. I've done some more research on these devices and one thing that concerns me is that in the descriptions of several they state that the resolutions of the 2 TVs need to be identical resolution or else one or both will not work. That's problematic for me since my Sony is 1080p and my Toshiba is 720p. I will keep looking but at this point I'm just going to stay with my current situation of manually changing the plug.
If someone finds a 1x2 splitter or distribution amp that is fully HDMI 1.3a compliant and can support two different resolutions, and supports all the HD audio, let me know! Thanks all for your help.