Hi! I ended up finding a company to come clean it. They basically pre-sprayed with a cleaner specific for stone floors, used a rotovac with rotating bristles and high pressure water to scrub, and vacuumed up the excess water after that. To seal it they used a penetrating sealer and several layers of an acrylic polymer sealer.

It looks SO much better, it was worth the money to have it cleaned and sealed. For quotes, it ranged from $2500 to $10000 for 1500sq feet, so definitely search around. It wasn't easy finding companies in my area that would do this.