Dear @kanchi647 : Your Cary line stage has other 7db of gain ( 24db. ) connected balancved.
You don't need any SUT even with 17db in the preamp you don't need a SUT.
The only reasons of why you are thinking the SUT need is because the cartridge has lower output than the specified by vdH or that your Phono Stage is out of specs that it's not given you those 39db on gain.
Any SUT will degrades the cartridge signal if the signal must goes through the Cary preamp.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.