So where should the tubes be?

They "should" be wherever you can access easily for maintenance.
Or not

I first added components designs using tubes in my Preamp and Phonostage, the CD player… then finally amp and DAC. The final switch to all tube equipment moved the system significantly to the musical end of the spectrum. Having all tubes just increased the realism and rhythm and pace so significantly… very synergistically. Highly recommended if well implemented.

Tubes should only be used where you want it to sound like music.

For me as it stands now:

Tube DAC
Tube phono stage
Tube integrated amp (had a tube preamp AND tube amp)

Don't let anyone tell you that too many tubes makes a system too "tubey" or too "warm" or "too (insert negative adjective here).

If the components are chosen wisely, tubes can be just as revealing and transparent as any SS counterpart. And you get what most SS can't give you, the emotional connection to the music.

And before you solid state guys start jumping up and down, I said "most". Some are better than others.

So tubes everywhere is a good thing.


Oz

Tubes should go where they sound good to you and work well with your other components.  It's really about your listening priorities.  I personally enjoy tubes in all my components and have speakers that respond well to tubes.  Some people really like the dynamics of SS components while others enjoy a mix.  There is no "right" answer and it's a question mainly of personal taste once you get past some general compatibility questions.  Don't let anyone tell you that only tubes sound like music - there is an entire market who only enjoy SS components and they are not "wrong". Such blather is ridiculously off-putting.