The M17 is a gorgeous beast, but the price is quite high unless you go to the used market. If your friend has a newer phone and isn't adverse to carrying 2 devices, the Fiio Q7 DAC/Amp might be an option to consider. If they went with the M17, they would likely be carrying 2 devices anyhow as most of us will take our phone with us when we leave the house.
At 40% of the cost of the M17 it's also a solid performer, having the capability of 3 x the output power - around 500mW for the M17, 1500mW for the Q7 on a balanced output with a 300Ω load. When used in desktop mode with the power supply plugged in, it can deliver up to 3000mW. Power certainly isn't the only factor and should really only be considered when using the unit with hard to drive headphones. With the nominal 20Ω impedance of the M9, either will have more than ample power to drive them to satisfaction.
A friend has a Q7 and it certainly performs very nicely with my M9, and drives my Sennheiser HD800 very well off the 4.4mm balanced output. I have the predecessor, the Q5s TC. It too performs very nicely with my M9 and HD800. Both are controllable via the Fiio Music (built-in on the M17) or Control app, with lots of filter and equalization options. The other difference is the DAC. They both use the ESS 9038 Pro but the M17 has 2 for running L + R channels separately whereas the Q7 uses a single one.
Both the M17 and the Q7 share similar accessories. It will come down to whether your friend would prefer a pure standalone player or if they want to use their phone as the player paired with the external DAC/amp. Personally I could not hear the difference between the Q7 and my Q5s TC, so the dual DAC configuration may be a moot point. I have only heard the A&K media players at a store and haven't spent enough time with any of them to formulate an opinion.
Oh, and I'm still waiting on a response from Sony and United Radio re: the protective foam inserts. I still haven't received the tools from my buddy to cut the foam inserts, but he said he'll get them to me this week. Had another paint chip appear on the right earbud of my M9 over the weekend. That's one negative of the M9 for me - it's certainly showing the signs of heavy use a lot more than most of my gear. If anyone else finds a paint that will adhere well to the magnesium alloy casing of the M9, I'd be curious to know which brand you used.