We all know that the Hifiman he6se has a high impedance...
50ohms is not high impedance. It's even lower than AKG's 62ohm K7xx line.
...it is difficult to drive with a normal portable DAC.
Well technically every headphone is hard to drive for a DAC, since the output stage of a DAC outputs a 1.2V to 4V line output without any current drive at all. And even if a DAC can get really loud driving a low impedance, high sensitivity headphone or IEM, since DAC outputs are meant to go into high impedance amplifier input stages, on dynamic headphones this can result in not just lack of current drive but also totally messed up damping factor when hooked up to a low impedance headphone.
You're going to need a DAC-HPamp, if you just want them all in one box, that way there's an amplifier output stage to drive the headphone. However...
I also do not want a desktop DAC that can only be placed at home, so I would like to know what you have to recommend.
My needs：
1) have multiple interfaces, 4.4 balanced / 3.5 / 6.35mm / XLR balanced
2) the price is not too expensive
3) light weight, can be put into the pocket.
...your next problem is that it be portable, not to mention small enough to fit in your pocket, is - well, to say it's a tall order is an understatement. But the problem isn't the impedance - 50ohms isn't too bad for amps designed more for current delivery and driving low impedance loads (ie even some desktop amps can end up with only 10% of the power at 300ohms vs what it can spit out at 32ohms or 16ohms), including portable amps running off a battery. However, the sensitivity is. At 83.5dB/1mW, asking for a portable amp - much less today's portable amps where RSA, Ibasso, etc balanced drive amps with way more power aren't the norm.* Heck, at 83.5dB/1mW, they'd be tough to drive for even desktop amps. Some newer NFCA amps can spit out power at a fraction of the price of the Schiit Lyr, so there's that, but they still need to be hooked up to wall power, not run off a battery.
Basically, chances are if you tried driving the HE6se with a portable amp it's kind of like taking a classic all-steel musclecar/pony car classic car body, ask for an Audi 1.8T engine, then be surprised that it's slower than an Audi A5 with an aluminum body and the 3.0L V6 twin turbo engine. And all that is just because of the problem with running off a battery like it's magic (kind of like how California thinks batteries are magic and started banning petrol cars while people can't afford detached homes where they can install their own home chargers). There's also how you can have a 4-pin XLR output (the mini-XLR on AKG headphones is only 3-pin and can't work in balanced drive with just one mini-XLR) and still make it pocketable unless maybe a winter coat or a pair of gangsta pants straight outta Compton (or a State penitentiary, complete with the halfway up the arse waistline).
Things will only get worse if you walk around with these or use them in public transport because the HE6se are open back headphones, meaning not only is it harder to get them to play loud and without the amplifier distorting, they're also not going to block any ambient noise since the rear of the drivers are way open.
In short...you'll either have to lower your expectations on the performance by several miles if you insist on using a portable DAC+HPamp. Or even separate portable DAC-HPamp plus a more powerful portable headphone amp-only unit strapped together, because you're gonna need way over 1watt per channel for these to get to a point where I can confidently assume you won't say it's not loud enough (that doesn't take distortion and noise levels into account just yet either).
*
For a number of reasons, like
a. IEMs getting market share and can be driven to their maximum performance with a DAP, and still sufficiently so by a smartphone, for those who'd prioritize not hauling one more thing
b. Dynamic headphones have been getting higher sensitivity at lower impedance. Not just closed backs for portable use but also how the HD58X and HD6XX have the same sensitivity as the HD580/600 and HD650 despite having half the impedance. (these used to be more directly related as per older coil designs)
c. DAPs taking over from ridiculous stacks like the Ibasso DB2 Boomslang2 balanced DAC and PB2 Toucan balanced amp.
