I'll try my hand at the second question. Yes, TrueHD only comes in 5.1.
At this moment in time, there are exactly 109 titles with DTS MA 7.1.
IIRC, many Marantz receivers cannot matrix for rear speakers when the HD codecs are output as bitstream. If you have the LG decode for you instead, then you may apply matrixing algorithms like PLiiX to have the rears active.
For that matter, these same Marantz models might not be able to apply Audyssey to these codecs as bitstreamed. Can't quite recall exactly, it will warrant some investigation. Well, you will know pretty easily I suppose, depending if you can see the Audyssey logo light up.
I am betting that if you set your bluray player to decode, sending out as mch PCM, you will be happier. No more "trueHD" or "DTS-MA" logos on the receiver is all.