Using existing public transport lines for HSR?

Hi all, forgive me if this is a stupid question.

I’m a GIS guy who moonlights part time on weekends and has very little to do on said weekends so I’m designing a very much conceptual HSR system for my old home state of Georgia to pass the time.

I’m trying to minimize impact to neighborhoods and reduce land purchase and construction costs when I can so an idea I had getting into Atlanta (since the sprawl is enormous, NIMBYS/HOAs abound, Atlanta’s dark history with redlining, and the fact that Atlanta sits on a granite plug makes tunneling unappealing) was to link the incoming/outgoing rail links to the existing MARTA track and basically turn the incoming HSR train into an “express” with one stop in the burbs, one at 5-Points, and one at the Airport.

Obviously this’d involve adding in additional tracks to get around the every-station commuter trains, but my question was more is there any kind of potential technical limitation to doing this? MARTA is standard gauge and 3rd-rail electrified. Some of the trains in the UK (where I live now) can swap between overhead A/C and 3rd rail DC.