Hello Mike,
given the fact that your application is adjustable to the x-former and that you are not matching impedance and only do voltage coupling, a 10k to 10k should give you the desired low end, if you deal with audio signals that have a lower short impedance of 600 Ohm (that is approx. 10k unloaded) and that is only when you are doing voltage coupling.
The high impedance of 10k will match up with any load and won't hardly produce and reverse magnetic field in the low end that might produce phase issues, or dynamic distortions.
On the other hand you need to shield the x-former at least with 60dB of magnetic shielding, otherwise your good low end will be overlaid with noise, EM/RF, etc.
But dealing with impedance coupling you have to get the x-former matched to an optimum of all impedance that need to be driven.
A general rule is for x-formers that are alike in ratio will have the same characteristic regardless of impedance, as long they are properly designed.
I hope that answers your question.
Best regards,