I don't think they will be necessary.

Use the one with less noise.

Beringer claims boutique style performance for its Xenyx preamps. But there is nothing wrong with running one microphone preamp into another. You will have to ensure proper padding & gain staging. Double preamping does nothing to increase clarity. In fact, it has the opposite effect. Your cleanest signal path is simply a straight wire. Anything else other than a straight wire imposes its own distortions & artifacts. But there are of course reasons to have 2 preamps cascaded the way you have. Of course you'll have the goodness of the tubes and its optical compressor. You'll also have the character of the boutique Xenyx preamps. But this won't work well if you don't have proper padding & gain settings. So since you are taking a line level output from your external tube preamp and feeding that into your Xenyx preamps, you'll need to reduce microphone trim gain & engage the pad. No pad? Without a 20 DB pad, you are likely to have 20 DB of too much gain or too much noise. That's unacceptable. So in this situation, you want your external preamp to feed your analog to digital converter directly or if you're utilizing the Beringer mixer? You should plug your external preamp into your Beringer line input.

I frequently have to take a line level source into my microphone inputs on my console because of the nature of my remote recording work. This works well for me since the console has built-in patting along with gain trim on a single control. So I can optimize noise versus headroom. In fact, some microphones splitters used transformers which are passes devices. While other microphones splitters are known as "active splitters" which actually contain a hopefully not to lousy microphone preamp that is then electronically distributed. I really don't like those because I'm getting the sound of a preamp that really is not up to par with my consoles preamps. Thankfully, my console microphone preamps are so good sounding, it transcends the lousy active Mike preamp splitter. But nothing sounds so good as just a single preamp. So for enhanced clarity remember: LESS IS MORE with a KISS a.k.a. keep it simple stupid.

This is another reason why most large-format consoles in control rooms have largely disappeared. Everybody knows, microphone to preamp directly to track. Here's no reason why you should send your signal through multiple summing amplifiers, output amplifiers, etc.. That's only necessary if you're combining multiple microphones to a single track. So now you know the best recordings are made with the least amount of equipment.

I've got the most equipment & the best recordings
Ms. Remy Ann David