My first post - 7.1 now you see it now you don't?

Hi, I hope I can get some help on this situation.

I have a JVC THX Ultra 7.1 receiver (RX-DP10) which decodes DTS-ES & Dolby - EX.

I have recently installed the two surround back speakers to take advantage of the extra coded sound in the 'back' speakers.

The strangest thing happens - I bought two DVDs as test discs to try:
1. Revenge of the Sith - Star Wars - which is THX & Dolby Digital EX compatible.
2. GoldMember - DTS 6.1 discrete.

I have the decoder set to 'AUTO Detect' on the receiver.

When I put in the Starwars disc it activates the Dolby digital logo. When the movie starts there is a quick promo for the THX sound which lights up all 7 speakers. This promo goes for about 20 seconds. Then the movie begins and the system drops back to 5.1. I cannot get the surround back speakers to work during the movie? Why is this so?

When I play Goldmember the DTS logo lights but again only 5.1 channels and the surround back speakers are not activated.

Why would the receiver activate all 7 channels during the THX promo and then turn off when the movie starts?
Why would the receiver not activate the surround back channels with a 6.1 DTS movie?
Any tips would be appreciated - it is driving me crazy!

Thx
Ray.

Re: My first post - 7.1 now you see it now you don't?

Try using the THX mode. Does the display read THX CINEMA or THX SURR EX? It's quite possible that the EX flag was mistakenly left off the DVD.

Hey Jeremy, thanks for your reply.
The THX mode does light up THX SURR EX and does project some sound from the surr. back speakers. However I think this is a simulated sound as the extra to speaker that represent a EX or ES signal still are not lit.

Tonight I tried another DVD, the animation 'CARS'. This lit up all the channels including the surr. back. It is a Dolby EX sound track. This was a relief as I thought the receiver was not working properly.

However here is the curious thing. I took the StarWars & Gold Member DVDs to my friend's house. He has a 6.1 EX/ES receiver.
The StarWars Disc performed as it did on my receiver, i.e. it lit up the Dolby EX light only during the THX promo and then went back to 5.1 when the movie started. Even though 5.1-EX was selected on the disc.
Gold Member however did light up the DTS-ES symbol, which it doesn't on my system - still can't understand this one.

Are there many discs that are miss flagged or more sensitive for one receiver to another for decoding? Being digital I thought it would have been on or off - no variation.

At least I have experienced Cars in Dolby - EX. However yet to experience DTS - ES discrete - I will have to try more discs.

BTW I did try a different DVD player on my system, which gave the same results. Even tried both coaxial & optical cables and again the same results.

I hope that different DTS - ES software will trigger the surround back speakers so I can at least be Physiologically satisfied.

Any other suggestions would be much appreciated.