Well, you've told us that you haven't been able to make it work, but you didin't really tell us what you've tried. For example, I don't know what "all the codes" on the JP1 forum means. But, on the chance that you haven't done this the easy way, I have gone to the DVD part of the hifi-remote FileSection, downloaded the DWM-370 (pretty close model number!) and the DRW-500 files, examined both in RM, and see that they use NEC1 protocol, device 60, subdevice 196.

Using the the Protocol part of the Lookup Tool, it turns out that an exact match is Video 0670 (20670), but that code isn't available in the red button remote, although it is in the grey one.

I also see that the red button remote has Video 0873, which is a 4DEV executor that provides both 60.196, and 49.206. Using RM again, it appears that the Power button is mapped to 49.206, but the number keys match 0670. So if the DWM-450 uses the same IR signals as the two above DVD players, then you can either use a grey button remote as is, or you can assign EFCs onto some of the red remotes buttons, like Power.

If you actually went through the above process, and found that NEC1, 60.196 isn't the correct protocol, then I wish that you had said so!