First off...

This Info is provided AS IS. I (Simon Noble) cannot and will not be
held responsible for any damage to your soft/hardware, if you do
what I am about to explain here. This mod is not for the light of hart, you
should have some reasonable soldering ability.

THE PROBLEM

Some MPro sound cards don't seem to be able to sample digital Audio without the channels swapping (at random) this can be seen best by setting the REC LEVEL of your DAT/(A to D converter) so that one channel is at a much lower level than the other, then recording some stereo sound with Samplitude, then when you view the wave forms for the right and left channels you will see sudden jumps and reductions in amplitude for the opposing left and right channels, Since my card is fixed I can't show a picture of this

Someone mentioned to me that the MPro lacks A "Low Impedance Ground Plane" this is usually where there is an internal layer in the PCB that is connected to zero Volts or GND at each of the chips GND pins, this is usually a solid layer of copper

Important point #1 Electric Current likes to flow back to GND from the chips on the card the same way that it got to the chip, so connecting any old wire may not work, it has to be like a flat PLANE across the whole card.

THE FIX

Well, I made a Ground plain from some prototyping PCB and soldered small off cut component legs to the MPro (see pic) these legs should be attached to the GND pins of all the chips on the MPro, I also did this to all the capacitors and any other component that had a Grounded pin, also where tracks passed through the PCB. This may have been over kill :-)

then having cut the Prototyping PCB into squares (to ease the fit over the cut legs) I soldered it down to the MPro

MAKE SURE THAT YOU ONLY CONNECT THE GND LINES ON THE CARD TOGETHER (test this with a continuity tester before you put the card back in you're computer) One wrong connection could destroy your computer. check and double check!

Important point #2. the Ground plain should be as close to the card as you can get it, mine was less than 5mm away. (see pic)

Lastly but not least you should connect all the tracks on the Prototyping PCB together, I made connections at right angels to the tracks with more component legs (see pic) these were soldered to each track.

there is probably a better way than mine if you have a suggestion or if you have any questions please Simon Noble