I'm not familiar with either preamp, nor am I willing to play in that tier of audio product, but . . .
At some point, possibly, maybe with two components such as these, aren't "improvements" more about preference and synergy rather than actual performance gains?
I'm not implying performance gains aren't possible, but at what cost for "substantial"? And of course each individual has to define cost versus value.
At the level of performance you're discussing here is it possible for someone else to legitimately suggest to you if exchanging one component will be an upgrade? I imagine you could even conceivably degrade the ultimate performance of your system, however minimally.