Yes, ATV is Apple TV.
STB, Set Top Box. As in the thing you pay the cable company $8-$12 per month for.
DPL, Dolby ProLogic(which this JVC has version II, which came out in 1987)
DD, Dolby Digital(which came out in the 90s...and is the "broadcast standard")
DTS...the other "better" sound format other than DD...found on disc media only(as far as I know...there is no DTS on streamed content...as it would be pointless. Streamed barely needs DD)
The age of your ATV doesn't really make a difference. Is it Gen 1, 2 or 3? (Apple doesn't follow "product year" like everybody else...for them...Gen 1 just means it "came out first". They did quit selling it "new" when Gen 3 came out...and Gen 1 DOES have an analog audio output...which is why if you search Ebay for Gen 1 ATV...you see they sell for double what a Gen 2 or 3 sell for)
So...in a nutshell, this hinges on your ATV. Once we know what it is...we can cut the confusion.