If your AVR does not have HDMI inputs then I would add a HDMI switch with remote control to connect the cable box and the Blu-ray player into. That will allow the single HDMI input on your TV to service both of those devices. I use this matrix switch:
4X2 True Matrix HDMI 1.3a Powered Switch w/ Remote Controller (Rev. 3.0)
That switch will allow you to actually output to 2 HDTVs and independently select the source for each TV. Later if you get a AVR with HDMI input, you can use the second HDMI output for the audio or a second TV later. That would allow TV use without having to turn the AVR on to watch TV.
Then for the audio connect optical cables from the cable box and the Blu-ray player.
If you use a programmable remote with macros, the matrix switch commands can be learned into it and macros set up to switch all of the devices as necessary.
Now if you don't think you will need the second output, this switch may be better for you:
4X1 HDMI 1.3b Certified Switcher with Toslink & Digital Coaxial port (Rev.2)
That will allow the two devices to be switched along with the audio for your AVR.