that's the best way to go, IMO.

I have prosound on a few regular DMG's and the drop is just too much.  So if it's similar to that, then it won't work for me.  But I just bought a third pocket that I will leave unmodded for writing and the prosound ones I'll use for recording and live shows.

You could go complicated and get a dpdt switch lol, that either completed the jumpers or the jump you create to the headphone socket (obviously not serious, but very possible). Seriously though I have noticed very little drop in volume, plus I can't stand a non-prosound turned up anyway. I recommend internal prosound like I did in my red boy. it works very well.

well, then do an external jack.

That's the problem, I don't want the headphone volume to be lower.  I don't want to drill holes into the pockets but I'd prefer an external jack.

your headphones will work with it, but the volume is gonna be lower. That's all. It's only a problem when you're making music in the Sao Paulo incredible noisy subway trains. That's why I use my prosounded DMGs only live, and have a spare one just for writing music on da streetz.

I recommend doing the internal prosound, i've yet to find a pair of headphones that won't work with it, whether on dmg/colour/pocket/light.

Thanks all that pretty much answered my question.  Except for one:  if I were to add an external jack, headphones won't work on it.  I'm aware of that.  But if I prosound a pocket using the original jack, do I lose the headphone capability as if it was an external jack?  If not, then I don't see the point in adding an external jack and I will just prosound it using the original jack.  But if I am going to lose the headphone capability by doing an internal prosound, then I just want an external jack.  The speaker is useless to me.  I can barely hear it anyway.

To clear up the question about internal and heaphones, with the internal version you do not need to remove the standard speaker as it shuts off when you Plug a line into the output, so headphones or a mixer, it shuts off the standard speaker. here's a picture of a prosound pocket board:
(also notice the removal of em2 and em3 jumpers, down near the jack)

If you are using the headphone socket then no, the ground is already connected. You just need to wire L and R.

Thanks for your answer InactiveX!
Sorry if it's a dumb question. If I haven't removed the standart mini-jack input and just wired L and R to the jack connectors, do I still need to run a wire from shield to a ground? I'm just confused a bit

its the same as the GBC.

I'll try to clear this up.

If you add a prosound mod, you can either use the headphone socket or add your own socket. If you use the headphone socket, ground will already be connected (otherwise nothing would come out of your cans) so you simply need to disconnect the other socket pins and route L and R to the socket as per photo above.

If you add a new socket, then that will of course need its L and R connected, and the ground pin must be connected to a ground (or shield in photo) point on the Game Boy board.

Ground points are all over the board. A multimeter can be used to find them, with a simple continuity test. Re Question, it's not for safety, it's essential for a circuit to work. Electricity, as every skoolboy no, is the effect of the flow of electrons. Think of ground as a drain where the electrons are collected up before being whizzed off back round the circuit again, flowing all the time. Disconnect ground, and the electrons cannot flow = no electricity.

I think it was originally done to give a signal at line level, to suit sound recording conventions. But I may be wrong. Also IIRC, the mod (tips hat to Trash80) was found to improve SNR on certain models of Game Boy. 1/8" is appropriate because it is a good fit for the Game Boy. It's not exactly the case that "the 1/8" prosound mod will decrease or even eliminate" the noise - prosound may help, but the choice of 1/8" is irrelevant.

Of course you should! Mine is always within easy reach! Hope this helps!

Exactly. Prosound increases the audio quality. Period. On the pocket it will reduce/eliminate the ground hum when recording.

While RCA and 1/4" are there to allow easier connectivity to mixers you can just as easily get a 1/8" to 1/4" adapter. Not sure what you meant by Suitable for midi inputs.

I am pretty sure the original intention of the prosound mod is to improve the sound quality.  That is why all of the modders out there offer 1/8" as a standard common mod.  When my pocket is running through my mixer, it puts out a nasty hum and I have been told the 1/8" prosound mod will decrease or even eliminate that.  I will try the connections that are shown in that picture you posted even though that isn't a pocket.  If it's doesn't work, I'll desolder the connection and try again.

Thanks.