On page 12 of the BD55 manual, it shows how to hook up the unit for 7.1 audio. Once you activate the unit for 7ch, it configures the normal L/R outputs as the L/R Back Surrounds. So, if you are playing a 7.1 soundtrack the Backs should then be active.
Most of us with just 5.1 systems will use the 2ch(Downmix) + 5.1ch configuration.
So, the question now is:
If I configure the BD55 for 7ch mode, run all seven cables into the 990, and the 990 only has 5.1 speakers configured, will the 990 downmix the 7.1 inputs to the 5.1 speakers configuration?
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Current Setup:
Samsung HL61A750 LED DLP RPTV
Marantz SR5004 AVR / Outlaw 7075 Amp
L/C/R: Ascend Acoustics 340M/C/M
L&R Surrounds: Ascend Acoustics CBM 170
SVS 25-31PC
Panasonic BD55K Blu-Ray Player
Dishnetwork VIP722 HD/PVR.