Reel to reel deck directly to power amp ?

I have an "old" Crown SS800 reel-to-reel that I use in one of my systems.  It has all of the inputs and outputs associated with a pre-amp and is what I run the amps with.  The difference with your Studer / Otari concept is it/they don't have any tone controls (yeah, I know, audio purists don't "do" tone controls.  I do.  Even have a graphic equalizer in my esoteric system - gasp!), which may make your listening a little strained.  The Crown also has Class-A inputs (courtesy of John Haynes, Goshen, IN - Wherever you are dear friend) that sound really great with older/vintage speakers.  I'm partial to co-axial/coincidental speakers also.  So good luck with the system and I look forward to hearing about what your hearing....brilliant!

One more cable plus transformer - this will degrade the sound. Separate phono with appropriate output impedance will be better. What is the good range of output/input impedance proportion, 1/5-1/10 or so ?

Ideally 1:10 or better is the rule of thumb.
It will be tricky to come up with a tube phono section that is OK driving 10K ohms. While the output impedance might look low enough on paper, the defining spec is what the output impedance is at 20Hz, not 1KHz.

That is why I recommended the transformers. BTW, input and output transformers are quite common in studio gear, from whence most of our recordings come. I don't like transformers, but they have their place and when they are needed, they can be really helpful!
Where will the extra cable be used??

Ralph, unless I got confused - one cable goes from preamp's tape-out to transformer and another from transformer to deck, as opposed to from separate phono directly to deck.
I think, my Nak's input impedance is around 50 kohm and my Acoustech's output impedance is close to 10 kohm, very high. They match very well, I can tell this.
Hard to find phono stage to impedance match pro or semi-pro deck...
Unexpected complication.

Most line-level impedances are 600-1000 ohms.  Tube amps input impedances are 50kohms to 100kohms.  Should work well.  Some solid state amps as low as 10kohms inputs .... not as much gain and frequency response issues if the nominal impedance rises sharply in the bass (as sometimes is the case).  Tube amps should be a decent bet.

Many preamps have 10kohm RCA line level input impedance, just like pro reel to reel decks. I haven't heard of many difficulties of matching separate phono's output impedance to that, though not all of them would match, of course. I think, both Al and Ralph exaggerated on this point. XLR line level input impedance, speaking of preamps not decks, can be much higher, I've seen figures of 40kohm. There are not many phono stages with XLR outs, though, and most that do are not inexpensive.
Anyway, I see it as a very workable minimalist idea and will get to it at the right moment.
My thanks to all participants.