Bill -
Mica's description of the mono mod is geared toward building a mono cable or adapter. I built just such an adapter cable (about 8 long) years ago so I could use my Series with a wireless transmitter pack.
You can do it externally like this, or you can do this inside your bass, if you don't want to have stereo out on the 1/4 plug. The only problem is that the 1/4 plug has a *lot* of stuff wired to it since it includes power switching for the batteries (I've seen a lot of guitar electronics and the Series wiring is probably an order of magnitude more complex than anything else you'll ever see).
Basically, you need to identify the neck and bridge output wires on the existing plug, then cut them, splice in the resistors, then join the two outputs together and connect them to the tip conductor of the 1/4 jack. It's really fairly simple.
You'll still have stereo output on the 5-pin connector (and you can still get mono at the power supply as you do now).
The one thing that you would want to look into is the circuit that switches between external power from the 5-pin connector and the batteries. I believe that this switch is part of the wiring on the 1/4 jack. If you're making this mono mod to use a wireless transmitter, then you probably want to leave the power switching alone (obviously, you want to be on batteries when something is plugged in here). You would want to make a change if, for some reason, you wanted mono out at the 1/4 jack but you also had the power supply plugged in. That's a pretty odd case - since you have the power supply connected, you can just get the mono signal at the DS-5. If you were thinking abou this mod in case you didn't have the power supply or 5-pin cable with you, then you really need to run off the battery. So, I probably wouldn't change the power switching part.
Good luck,
David Fung
