Headphone systems are a different breed from main speaker systems. It is probably better not having a preamp with a headphone jack. They tend not to sound good, even on high end components.
I spent fifteen years developing my headphone system from meager beginnings. You can see where I landed in my virtual systems.
The best way to get started is to get a headphone amp and connect your preamp output to it. I highly recommend Woo headphone amps if you like highly musical and detailed music. Searching for the right headphone amp is every bit as hard as finding an amp for your main system. If you get serious about it is likely you may choose implementing a separate system. But the key is a headphone amp… and compatible headphones. Great headphones like Sennheiser 800’s require tremendous power and natural balanced sound. Others like Focal and UltraSonde require far less power, but still really natural sound, unless you like “details are all” kind of systems.