Integrated Tube Amps with Subwoofer out?


I’ve only seen subwoofer outputs on a couple of integrated tube amps (Rogers & Rogue) why is this so uncommon and are there any others I should be looking at? 
The Rogue Cronus Magnum III has a phono stage too, which make me like it even more. 
valjean246o1
Rogue Audio Cronus Magnum integrated amps have a variable output that can be used for subwoofers. That's what I use and it's fantastic!
Black Ice Audio (formerly Jolida) has a new line of integrated all-tube amps that all feature (mono) Sub outputs.
I’m using a Line Magnetic LM805ia (not equipped with sub out) with DEBRA sub array. I have a line out conversion recommended by James (company owner). This is the same/same millercarbon mentioned. I used high quality Vishay resistors. Problem solved.