I've always pronounced it A-D-I-S-C. I didn't even know others pronounced it A-Disc until years after I joined. For some reason, A-Disc just doesn't sound right to me, so I'm going to keep pronouncing it as A-D-I-S-C.
Seems like most people either pronounce it speaking out each letter, or "ay-disc/a-disc" and it would have just been interesting to see which was higher. The post seems to imply a leaning towards ay-disc .. which I think makes sense.
I'm also one of the people who say "ay-disc" because I find it has a more natural flow in speaking conversation and do believe that it makes sense that it does. If an abbreviation does this is generally just about if it's possibly to speak it naturally in English as a word.. which is generally reliant on there being vowels present. Which ADISC does have. People say out MSNBC.. or NFL.. but that's because there is no good way of turning that into a spoken word due to lack of vowels. However most people say PETA like "pee-tah" because there is.
in 'supposed', you would used the same sounds as how they're used in the words they're shortened from; so, both short vowels.
and once again, a long 'a' [A] is pronounced 'A', not 'eh', 'ey', 'ay', 'aye' or owt else, and a short 'a' [a], 'a', as per the principle of an Alphabet by which single sounds are represented by single letters.