[G4] G4 DA and USB Speakers

[MnVikes]

Does the use of USB speakers on the G4 DA task the G4 CPU more than if you
use the regular (analog) speaker output? I'm thinking of adding Apple Pro
Speakers to the G4 Digital Audio, but I want to know if it will slow down
the computer. Likewise will adding a USB microphone add to the G4's
workload?

Second set of questions: I've seen some ebay auctions for MDD dual processor
cards. Will they work in my G4 DA?