From my perspective: CD is the go to format for stereo. Vinyl doesn't compare, can't see why anyone thinks it does. MP3 is Ok for portability (Though Sony's Atrac was far superior, with better sound and gapless tracks) but downloads are, to me, inferior in any format. I'd put them on CD cos having them on computers, memory sticks or whatever means having to find them. My CD's are alphabetical or in a Discgear unit.
5.1: DVD or Blu Ray, don't mind which, it's not going to make a huge difference to me, my system is good, but uses small JBL speakers, so it's not as high fidelity as my stereo, it's just nice to hear stuff in surround. SACD is dead, really, it never caught on, and it's on the back foot now!
I could go all day about this I think it justifies a thread of its own . Am opening one in the forum of the last resort.