The 326S is a very good preamp; I owned one for many years. It's also the best designed preamp in terms of user interface I have ever used or tried. Having said that, the Ayre KX-R was clearly better and it's not even in the ballpark of the KX-R Twenty. Given that the KX-5 Twenty reportedly rivals the performance of the original KX-R, I expect that I would prefer it the 326S. On the other hand, the K-5xe is now a couple of generations old and I don't expect that it will be able to keep up with the 326S.
Irrespective of all that, given your preference, I expect that you will find that the 326S will be a clear upgrade to what you have now and might even be your preference irrespective of the performance of the KX-5 Twenty. Be aware that while the 326S still has that typical Levinson house sound it has much less of it compared to earlier products.
I don't think you can go wrong with the 326S.
Irrespective of all that, given your preference, I expect that you will find that the 326S will be a clear upgrade to what you have now and might even be your preference irrespective of the performance of the KX-5 Twenty. Be aware that while the 326S still has that typical Levinson house sound it has much less of it compared to earlier products.
I don't think you can go wrong with the 326S.