The skin depth in copper at 100kHz (the upper BW of most good audio amplifiers) is 0.2mm so this equates to a 32AWG wire. Assuming you want the equivalent of a 12AWG speaker cable then this would equate to the need for 103 individually insulated strands of 32AWG wire to make the equivalent of 12AWG.
The Litz design that I am considering would be based on using 108 individually insulated strands of 32AWG wire. From a practical construction perspective I would suggest that the individual insulation is colored - say red for the positive and blue for the negative.
The Litz wire would be made in three levels:
1) Take 3 red and 3 blue 32AWG strands and twist them together to form a 6-bunch. Make sure that the strands are alternated - red, blue, red, blue, red, blue.
2) Repeat step one 36 times to result in 36 6-bunches. Each 6-bunch should be twisted the same way (e.g. clockwise) and the number of twists per length should be the same for each 6-bunch.
3) Take six 6-bunches and twist these together to form a 36-bunch.
4) Repeat step three 6 times to result in six 36-bunches. Each 36-bunch should be twisted the same way (e.g. counterclockwise - the opposite to what was used for the 6-bunches) and the number of twists per length should be the same for each 36-bunch.
5) Take six 36-bunches and twist these together to form a 216-bunch. This should be twisted the same way as the 6-bunches (e.g. clockwise).
6) Apply a length of woven expandable PET sheathing over the cable to provide some physical protection for the finished speaker cable and secure each end of this sheathing with a short length of heat-shrink tubing - approximately 100mm from the end of the cable.
7) At the 100mm ends of the cable that are not covered in the sheathing separate out all the individual strands into two bunches - 108 red wires and 108 blue wires.
8) Strip 25mm of the insulation from all of the individual strands.
9) Twist all of the blue strands together to form the negative speaker wire and twist all of the red strands together to form the positive speaker wire.
10) Enjoy!