Tube Integrateds...why not a preout for subs.....

Hello. I always wonder why tube integrated manufacturers do not provide a preout for the use of a sub. Truly, anyone that is using a tube may be 'purist' and not use a subwoofer. Truly, I would, but I am using a hybrid amp/preamp.

My problem is with trying to get my friends who say they can't spend much to get them into what they would love. I can't ask them in one swipe to spend more than $1500.00 for the amp section. It is simple wiring. And if you want to introduce someone....I am just saying. Any ideas?