It sounds like the issue you're bothered by is uneven dings and divots, etc. that weren't covered by the coatings you've applied so far. Often those imperfections can be masked by flakes, but that's not an option for you.
If you want the final floor to both look smooth and actually be smooth your best move is to put down another coat of the pigmented epoxy. First scuff up the existing coating, wipe it with denatured alcohol, then mix up a bit the pigmented epoxy and literally flood the divots and low spots. Pour out enough to bring those areas up to grade. Allow them to get tack free, and then coat the entire floor with about 4 mils of the epoxy, you don't need than much since you already have a base coat, you're just applying another layer to have a nice seamless finish. Finally apply your optional clear coat with the grit additive.
I'd avoid sand, it's sharp edged and not the strongest grit, it will crush and crumble. Rather use polymer grit, it has rounded edges so it won't shred mops, paper towels, and skin.
Also not a big fan of polyaspartic for DIY, and even our contractors aren't big fans of it. Its big advantage, almost its only advantage compared to good epoxies or polyurethanes, is a quick return to service. On the downside it's not easy to work with, it has a bit of a learning curve, plus it's costly.
But before you do anything you really should consult with your supplier.