Unfortunately there’s almost zero market in hifi for the intersection of these things, so anything you come across that gets close is almost certain to use low cost off-the-shelf chip based solutions for most (if not all) of the functions you require:
- Headphone amplifier with low impedance driving capability (32 - 300 ohms) compared to a traditional preamps. The throw-in headphone jacks you see in DACs, receivers, preamps, integrateds (and other such products) are sometimes serviceable, sometimes AWFUL, and almost never near the best of what you can get from headphones.
- Volume with balance control
- RIAA phono stage and MC headamp
If you care about quality (which is presumably why you’re here), you’d be far better off with a dedicated phono stage plus a dedicated headohone amp, each of good quality with discrete circuitry. Schiit Audio makes this kind of stuff with a good bang-for-buck. I would also recommend Hagerman Labs - more for the phono side there, but he does have a headphone amp too. I’m an old head-fi guy and if I was starting from scratch today I’m getting an old dynalo (Kevin Gilmore Dynamic), dynamid, dynahi, or GS-X build, whatever I can find, and calling it a day. Maybe an EARMAX or similar OTL if I want to go the other way and wallow in glorious double-digit distortion. Maybe both! But getting a balance control too is going to be tough, without adding a 3rd box and degrading quality with a cheap potentiometer.