Whoa, off topic.
Your best bet would be to stick with bitstreaming the DD5.1 and DTS 5.1 soundtracks. If you go down to 2 channel then you are losing all the discrete surround effects. I can't tell a difference between HD audio and the DD and DTS lossy versions. The differences are pretty dang small. Remember also that BDs use the full bitrate available to DD and DTS while DVDs used more compression. So, your BDs, even in DD and DTS will still have higher quality than most DVD audio.
When you are removing the surround encoding by downrezzing to 2 channel, you are losing a lot more than a bit of dynamic range audible only to golden ears, you are losing 3 full channels of positioning information and that is most certainly noticeable even by untrained ears.
