You've got lots of options.

Shimano freehubs are the same width for 8, 9, and 10 speed cassettes, so the simplest way to go would be to throw an 8 speed cassette on your Zipp wheels (likely without any modifications or spacers) and be ready to roll ...after adjusting the rear derailleur to account for the wheel change.

Or you can upgrade the shifters to 10 speed and use a 10 speed cassette. The bike's current derailleurs, if they're "8 speed" models, have the correct cable pull ratios to shift a 10 speed drivetrain.