Yup discontinued, dolby digital decoders are now longer produced, although there are av pre-amps, but there are quite expensive, and have video switching. Do you need video switching?
I have a Denon lying around. There's the Harmon/Kardon ADP-303, that's a stereo & Dolby Digital decoder, it's not as well featured as the Denon. No remote control for one, and it doesn't decode pro-logic. I have a ADP-303 spare too.
You could look at a budget av amplifier, as they do the same job as the denon, plus have newer dsp decoding, dd ex, es, pro-logic II etc. Make sure it has a full set of pre-outs (5.1 analogue) otherwise you can't use your Logitech speakers.