Firstly welcome to the Decware family and congratulations on your impending UFO25! I hope that you'll agree with me it is worth the wait and worth much more than the price. Now I'll give you my thoughts on your situation, with the understanding that I haven't actually heard any of the gear you reference. But I am a big fan of Luxman and familiar with the "house sound."

I'll start with this: I can't imagine having a system in general, and specifically with a UFO25, that doesn't have a tube preamp. So of your choices I would lean toward the CL38. But that is me. One thing to consider is the UFO25 is likely (much) more transparent than anything you have heard before and the quality and/or weakness of everything in front of it with be highlighted. So, while I might lean towards the tube preamp I would suggest you may be better off starting with the pre-out of your current amp at least until the UFO25 is broken in and you have better idea of the sound you want in front of it.

FWIW, my audio journey is much too long for this post I'll mention that before Decware I had a long term relationship with Pass Labs monoblocs and an AR LS25 MKII preamp that I thought was the last word in transparency and timbral accuracy. I literally wore out the Pass amps, and got Decware UFOs hoping they would give me something close at a price I was willing to pay. And I was shocked, shocked that they blew my previous, Stereophile approved system out of the water. It was so good I got back on the waiting list for UFO25s and I couldn't be happier.

Regardless, please keep has posted as your journey continues.