Glad to hear you like the splitting, and thanks for your purchase!

It's not really possible to remove the borders when maximized to a split, these are just a side effect of faking out the maximized windows to constrain them to the splits.

You could try the "Remove Borders and Caption From Window" scripted Function (click "Download Scripted" on the Settings > Functions tab to find it), but I'm not sure that it will work on maximized windows.

Thanks!