Maybe I'm missing something but I don't think the Luxman will work for what you are trying to do. It is simply a speaker selector with only one amplifier input. The Douk is also not the answer because it is designed to go between the amp and the speaker. You need something that has one source input for your preamp and two line level outputs to go to your amplifiers. Then you need an additional selector to direct the speaker level output from the one of the amplifiers to your speakers. The Douk could serve as the second selector but there is a better way.
+1 for Mapletree Audio. You specify exactly what you want and they build it to your needs. I have one and it is looks nice with a retro vibe, is built solidly, and is noiseless. As @alucard19 mentioned, Al Freundorfer is very helpful and he can build you a switch box that will do everything in one chassis. It isn't cheap but it's by far the most elegant solution. If you explain to him what you are trying to do he will custom build exactly what you need.
When you set this up you should use a consistent turn on/turn off procedure to protect your tube amps. With the amps off, set the switches for the amplifer and speaker output and then turn on the amp once everything is properly switched. As with all proper audio hygiene make sure your preamp is muted when you turn on your amplifiers.