The problem with 480 2x is that it’s 960 which isn’t a standard resolution supported by most TV’s. This is what makes the DChdmi so appealing is that it outputs the 960p image in a 1080p " window" so basically any tv will pick it up and you’ll get the correct scaling and aspect ratio!
What black bars ? On the sides ? The Dreamcast doesn’t output a 16:9 resolution by default, but some do with GameShark codes.
My TV supports 480x2 just fine, it picks it up as a PC and the only real difference is the scanlines are much smaller and tighter then 480 passthrough. It looks like the DC does on a VGA monitor which I prefer over the straight passthrough.