There's no internal "mod", at least not an easy one.
There is however something called "DCHDMI" available now, which is basically an FPGA that gives true digital output from the Dreamcast.
The Pound cable is just an upscaler (and a cable), so picture quality from the new DCHDMI boards should be a lot better as it's digital->digital, but also a lot more expensive.
https://shop.dansprojects.com/dchdmi-pre-order.html
They seem to be taking pre-orders now?
These are tricky to solder in, the FFC cables and soldering points are tiny, and does require some experience, but you'd probably have to get the board before you can have it installed.
You could get an OSSC or Framemeister instead. Those are upscalers as well, but much better than the $30 Pound cable, and can be used on other consoles, like a Neo