The benefit of the NL mono out mod is that there's almost no line noise. It really is a nice clean sound. Having said that though, and especially since I haven't added a resistor to mine so it's unusably hot (not sure which value resistor is appropriate!), the prosound out is usually good enough on a DMG.

you probably could add a mono audio jack wired just to pin 31 (Vin) if you really wanted in addition to prosound jack, but you wouldn't need to, the typical prosound already includes NL mono audio. according to the schematic notes, maybe Vin hasn't been tested on SGB, but i am under the assumption that it works as intended

I've got all the stuff needed to try this.  SNES, Super gameboy, NL Mono, soldering tools, security bits.  Anybody wanna join up  to see if we can get this working?

One of the pins on the NL mono is a direct audio out. It is really hot. I.D have to dig around to see what pin exactly, but you could add an audio jack with the tip connected to that pin in your Game Boy Player. I don’t see why that wouldn’t work.

I asked Oliver awhile ago about this and the answer is that it won't fully work.

I asked if there was a direct audio out mod like on other Non-DMGs, but I never got an answer.  I know a Super Gameboy can be prosound modded, but don't know about the audio out pin mod.

probably would work with a super gameboy though

Since it doesn't work well with GBA, the probable answer is no.

Im interested in buying a NL mono cart. Does anyone know if it works with the Game Boy Player?