So, you're saying that your Anthem AVM50 does not decode DTS-HD Master Audio & Dolby True-HD found on bluray discs?
The AVM50 can't be that old and I would think it would be able to support and decode those lossless HD audio formats on bluray discs. Even if it can't you can still use HDMI and set the HDMI configuration in your Oppo to output LPCM instead of bitstream for those bluray's lossless HD audio formats, so that way the Oppo will decode those DTS-HD MA & Dolby True-HD and sent them hi-rez LPCM via HDMI to your Anthem AVM-50. But for regular lossy Dolby Digital & DTS you can set the HDMI configuration in the Oppo back to bitstream.
The AVM50 can't be that old and I would think it would be able to support and decode those lossless HD audio formats on bluray discs. Even if it can't you can still use HDMI and set the HDMI configuration in your Oppo to output LPCM instead of bitstream for those bluray's lossless HD audio formats, so that way the Oppo will decode those DTS-HD MA & Dolby True-HD and sent them hi-rez LPCM via HDMI to your Anthem AVM-50. But for regular lossy Dolby Digital & DTS you can set the HDMI configuration in the Oppo back to bitstream.