I use a similar setup with an Anthem MRX 540 and Luxman 509ux.
Here's what I think you should do though. Use a digital optical cable from your TV to your MXA70 to get perfect stereo TV sound.
If you still want to add surround sound, the MRX 540 or 740 are ideal enhancments. More information on page 26 and 27 of the MXA user's manual under "System Thru Operation."