I doubt that damage will result from connecting two line outputs, but anything is possible. If you did this to two outputs of your -power amp- then damage would certainly result.

Altec, you mean the power amp will be damaged if play both player at same time?

No. I was trying to make the point that you never want to parallel the outputs of two power amplifiers, as this will cause harm. This has nothing to do with what you are doing.

Altec,
I still do not understand why you pointed out your point of parallel the outputs of 2 pwer amplifiers" if it has nothing to do with what I would do. Please explain in layman term. I am no electrician. Excuse me ignorance. Thank you.

In my thinking, hooking up 2 dvd players' 7.1 analog output cables,using the Y-cable splitters, and contact to the same 7.1 analog input ports of 990 (i.e. sharing 990's single 7.1 analog inputs by 2 dvd players), shall not be a problem, as long as I do NOT play both dvd players at same time with the 7.1 analog outputs.
Besides, The 990 has selection of which 7.1 analog input which dvd player per pre-allocation (i.e. video 1 for first player & video 2 for second dvd player respectively). In this case 990 will never take in 2 analog outputs from both players at same time and send them to the power amp. Even 990 mistakenly send both analog signals from both players to the power amp (which I do not think it will happen), the power amp will shut down itself if the input signals are not "safe" to the power amp itself.
I buy your point that to play safe, by unplug 1 set of the 7.1 analog cable from the Y spliter when using the other 7.1 cables, which is combersome. That's why I prefer permanent hooking up if my thinking is right.

What is your furher expectised opinion.

Gonk, Scott and other outlaw memembers - well come to add in your comments. Thank you all.

Kwok

Hello Kwok,

As has been mentioned here, using Y-adapters to enable two separate source components into the same input is highly discouraged. Even while powered down, the "unused" source will be seen by the processor/receiver as a bad load. I would encourage you to consider a multi-channel switcher. I believe Zektor still manufactures one that may meet your requirements.

Best,

Scott

Let me toss out a less expensive option to the Zektor 7.1 switch that I think might work, since only one of your sources has a 7.1 analog output (the 981HD being 5.1 analog):

Use a component video switch or a similar unit to provide 5.1 analog switching between the 981HD and the front/center/side surround/sub channels of the S550. As mentioned previously, you'll be using a combination of component channels, composite channel, and left/right analog channels to handle the six analog audio connections. Then connect the back surround channels of the S550 directly to the 990. When using the 981HD, the back surrounds would appear to be unused channels (similar to what my 983H does when decoding a 5.1 source via the 7.1 analog outputs) - or at worst (if you had both players running at once) you would get back surround data from the S550 and realize that you ought to at very least pause the S550. It's less elegant than the Zektor, of course, but it will also cost several hundred dollars less...

Altec, Scott, or anyone else see a potential pitfall in this scenario that I'm overlooking?

No, actually what I'm hearing from both Altec and Scott is that this arrangement is not recommended because the Y-cables create a direct bridge between the two players' output sections (something that the designers of the players and the processor do not expect to see happen) and they do not recommend creating that condition. It is likely to create audible distortion, and I don't think the risk of actual damage has been entirely ruled out. If there were to be damage to the 981HD, S550, or 990 as a result (although the 990's comparatively safe in this situation, it sounds like), I doubt any of the companies involved would treat it as a warranty issue if they knew how the system was connected at the time.
The 7.1 direct input cannot be assigned to different sources (it is a source unto itself, with its own video input assignment available), and since it is a single connection it will have no control over what portion of the incoming signal is passed on - if both players are on and playing, it will pass both signals in some sort of unappealing summed mess. Even without taking that into consideration the amp won't know or care what's happening prior to the 990 - it will play whatever the 990 puts out.

Altec's comments about amps were not directly related to what you are proposing - they were simply applying the same electrical principles to a slightly more extreme case. He was describing the case of connecting two separate amplifiers to the same speaker, which is basically just moving the Y-adapter down the signal chain a step or two. Think of two separate systems (such as a stereo setup and a home theater setup) that share a room and a pair of speakers. Connecting the amp output from both systems to the same speaker would mimic what you are talking about doing with the 981HD and S550. In that amp/speaker scenario, the risk of amplifier damage is significant. Doing it with players and a processor may remove risk of damage, but you still get the distortion that Altec warned of.

I can attest to this. Last year was asked to diagnose a problem in a boardroom av setup. Some networking guy set it up so that a dvd player and computer dock were connected across the room from the big flatscreen, and used y cables to send both sets of signals through one set of 75ohm cabling. We had to replace the DVD player, and the rca audio on the computer was dead (still could use the headphone jack, though). Fortunately, they didn't share the same video signals...

Ouch...

Hay, Guys! Extremely appreciated all you warning and recommendation. Yap, use the component switcher recommended by Gonk should be the right and cheapest choice. I will go ahead to get one from Monoprice, to do the switching of 5.1 analogy btw 2 players.
Only the back surround analog inputs at 990 will be used by the blue ray hook-up, not the other player.
Gonk and Scott - then how about when 990 sending 6.1 signals upon PL IIx or DTS Neo:6 or 7-ch stero by the 990 processing. We haven't talk about this if using the component swticher.
Sorry to bother you guys.
Kwok