Old fashioned DD5.1 on Samsung BDP-1500

[rainman20]

Confession: I'm a newbie that just upgraded (partially) to a Samsung HD Plasma and BDP-1500 Blu-Ray (from old CRT and DVD). Partially, as I am still using my 10 year old Yamaha RX-V2092 workhorse that only decodes DolbyDigital 5.1 (no DTS or newer HD formats) via the optical connection from the BDP-1500.
SD DVDs are able to pass on the 5.1 audio just fine when I use the re-encode feature w/downgraded audio rate. BUT... in the two sample BD's I have (Ratatouille and Departed) which both claim Dolby 5.1 soundtracks, I cannot get an old fashioned 5.1 stream recognized by my Yamaha. I've tried various combos of audio settings on the player and can only get audio from PCM streams of what seems to be 2 channel audio. Do I really need to shell out for a new receiver for TrueHD/DTS-HD when I'm still satisfied with compressed audio at 5.1 or is there some way to pass on DolbyDigital 5.1 over the optical connection. Thanks!