The Samsung does not support any advanced codecs. If you select a lossless PCM track on the title it should give you that just fine out the analog multi-channel. It seems best to have both hooked up, or that is what many report anyways. I generally thought the 5.1 analog output was fine while I had it hooked up that way though.
Is this your first time using yoru 5.1 analog inputs? Generally you will find the levels very low compared to coax/optical, and the sub channel may need a lot of trim volume to perform as expected.
Generally what you end up with is better audio at a lot lower level, and will have tirn the main volume a lot more to make it loud enough.