Uh, I think you're missing something. In the "HD rerelease" they didn't change any models, and changed maybe like, 10 textures tops, most of which are unrelated to actual gameplay. It was just a matter of "hay gaiz download DX dlc and we'll unhide the 'mission' option from the main menu!"
Edit: I suppose they changed the look of the menus and things (slightly), but that's hardly anything worth noting.
Unless of course you mean SADX itself... in which case, SA2B is essentially SA2 with enhanced stuff (SA2DX)... Unless of course, I'm missing something here, but I'm certain the XBLA version of SADX is exactly the same visually regardless of whether you have the "DX DLC", and I'm also certain that SA2B is essentially SA2DX, so it's already got you covered.