It's been about a decade since I touched a DS Lite and I've never actually used a DSi before, so I can't say for sure, but I just read this comment on Youtube:
The new DSi is the first Nintendo handheld to have true 16 bit 44-khz output. Athough the GBA and DS fat/lite supported 16 bit internal mixing the older systems only had 8-10 bit output creating a hissing artifact which the DSi no longer has.
I've been tossing around the idea of getting a DSi XL or a 3DS XL. The DSi XL is still pretty expensive since Nintendo doesn't make them anymore, but the bronze color is gorgeous, and the 3DS XL colors just look kind of cheesy. Still, I think the 3DS XL is a good deal at $200. I think I'm just going to start snatching up some DSis off ebay and start mixing them all together.