The 15-1994 regards DVD codes as VCR codes, so in order to use AUX2 for the DVD player, you would first have to re-assign it as a VCR button, like this....
[SETUP **] 992 ** VCR AUX1 **
Then it will accept the 0503 code. If haven't already checked out my version of the manual, you should do so, it's on my site, there's lots of extra stuff like that in there.
Rob.
http://www.hifi-remote.com