Besides No.10 Bernard Foley, the Wallabies' inner and midfield backline is dominated by Brumbies players.
Nic White is the incumbent scrumhalf, Matt Toomua wears the No.12 jersey, and Tevita Kuridrani plays at outside centre.
Yet the strong performances of the Waratahs backs in Super Rugby's latter stages have presented McKenzie with a conundrum ahead of the Bledisloe Cup opener in Sydney on August 16.
Halfback Nick Phipps put on a sterling defensive effort in both the semi-final and final, Kurtley Beale lit up the park at inside centre, while No.13 Adam Ashley-Cooper's two tries in the final earned him the man-of-the-match award.
"There's always selection headaches," McKenzie said.
"The Waratahs have done a fantastic job, we recognise that, we recognise form.
"They go about their business a certain way, we do things a little bit differently.
"We'll go through the business of selections and announce a team next week."
With Nick "Honey Badger" Cummins off to Japan, it's likely Ashley-Cooper will stay on the wing for the Wallabies due to a lack of depth in the position, while Toomua's strong performances for the Brumbies should see him hold off a surge in form from Beale - who is listed in the squad as a No.10.
That leaves Phipps as the most likely Waratahs back to earn a starting spot - especially when one looks at his blossoming partnership with Foley.
Incumbent White performed extremely well for the Wallabies in the clean sweep of France in June, and was instrumental for the Brumbies in their knockout matches against the Western Force and Chiefs, but was outplayed by Phipps in the semi-final.
McKenzie, however, was giving nothing away.
"(Phipps) has done nothing wrong. All you can do is go out and play well every week," McKenzie said.
"It's up to the selectors to work out what we need in the circumstances.
"The difficulty for us is that some players will miss out."
The 11 Waratahs in the 32-man Test squad joined their Wallabies teammates in Bathurst on Wednesday for the Bush2Bledisloe campaign drive.
Both Toomua and White welcomed the competition created by their rivals.
"Maintaining combinations can only help a team," Toomua said.
"Whether that's the Waratahs' combinations or what we went with in the (France) Test series - I don't know.
"But to have those guys playing well and pushing for spots is only a positive."
