My question is: will the Digital's power quality end up suffering if I go from outlet -> Pedal Power 2+ -> Pedal Power AC -> Pedal Power Digital?
No problem whatsoever in doing this. It is perfectly acceptable to chain these three power supplies together using the Courtesy Outlets found on the other two units. In fact, you can power 10 more Pedal Power units after the first one before you come close to the stated 200Watt max on the Courtesy Outlet.
Why did you not include an AC outlet o n the Digital
One of the power supplies had to be last in the chain... we just made the decision for you!