Welcome. AR is a great forum with lots of tech guys. The forum isn’t filled with tons of posts but with the technical guys on the boards your going to get first hand experience.
A few thoughts. depending on your end goals maybe try contacting JHM they have an in house RS5 that they bought eairler this year and knowing how they beat on there car they would have first hand experience on what they saw and what they found necessary. I know they are doing a bunch of performance mods to the car in house so that would also be something that might cross over and give you a few options as well.
IF you do reach out to them let us know what they say.
As to your question.
There are the two parts to your transmission.
The hydraulic side that takes ATF and the gear side or diff that takes gear fluid. So lets just call it the gear side.
According to Audi themselves and there maintenance schedule
DSG/S Tronic® – change MTF oil for gear box l RS 5 only = the first 15,000 then every 40,000
DSG/S Tronic – change ATF oil and replace transmission filter element
for clutch hydraulics RS 5, S6, R8 Coupe only = every 35,000
This is directly from Audi. knowing that the rev limit is so high it would make sense that you have to service this gear oil more frequent than other cars but from what I have seen these trnamissions have been plagued with issues so I would make sure to be ontop of the gear box oil changes. And there have been reports of issues for people who don’t change the filter at the 35k
So the answer is you don’t need to do both according to Audi. The mechanical side makes the most sense due to the higher RPM the transmission is running under and those conditions will break down the gear oil quickly.