OK, the speaker level i/o will work fine, but then what happens when I want to watch a movie, the RCA mono will be the one to be used. As I understand, a sub should not be connected using both the inputs as there is no pre-amp in a sub to do the selection. So I will need to change cables every time the usage changes. Secondly, if the sub is off, will the signal still go to the speakers?
Your statements are confusing. I think we are talking about two different things here. One is the connection between the DVD/CD Player and the AVR and the second is between the AVR and the sub/speakers.
If you want the AVR to decode movie sounds, you
MUST connect the DVD Player using a digital co-axial, a optical, or the HDMI cable. When you connect a CD player, you use a RCA cable pair and connect it to the front L&R of the AVR. Remember one thing, you can connect a DVD Player through
both the digital connection for multichannel
and the stereo RCA cables for stereo music. Depending upon what media you use and what you select in the AVR (DVD or CD), the DVD Player will either send full digital signals or stereo analogue signals. Again this is recommended only if you are positive the DAC and other features of the DVD Player are superior to that of the AVR.
As I mentioned in the previous post, unless you have a highly advanced sub, it does not make sense to connect the sub any way other than the LFE of the 663. The crossover of the AVR will, in most cases, be superior to that of a regular sub.
You are correct in your thought that the sub can be connected only one way. And no, the sub's crossover will not work if the sub is off.
Using Straight mode or 2.1 stereo mode does not match up to the quality in pure direct mode, pure direct sound quality is far superior. so its not an option unless everything else has been ruled out.
The stereo and pure direct are identical in terms of internal circuitry. The only thing Yamaha does additionally in pure direct is to switch off all displays excepting a small green LED. This should not make any difference to the sound signature.
If you want 2.1 for music, you can use the straight mode, or route the speaker level output of front L&R from the AVR to the sub, and make the sub do the cross over. What works better depends a lot upon the quality of the AVR and the sub. There is no other way unless you buy an external bass management unit such as one made by Outlaw Audio.
For those of you who want to listen to two channel music from all speakers of a 5.1 or 7.1, you can set the AVR to use NEO 6 where it will send the audio signals to all speakers. There is no decoding or anything. The sound is just sent to all speakers. If you want proper multichannel music, you have to use a DVD-A or a SACD on a player that understands these media.
Cheers