Thanks, Charles.

One thing for the realisation, I kept a separate line for signal and "power" ground - for your schematics, I would power the LEDs and the shift registers separately. Oh yes, I incorporated the shift registers into the "cable"...

The software is here: http://www.8052.com/users/wek/xmas1.a51
Quite dirty, beware.
A couple of issues:

• for Charles' schematics, change the "polarity" of Data0 and Data1 - simply cpl-ing them before shiftout
  
• I used P89V51RD2 which has hardware SPI, so the clock line is at P1.7 and the data (MOSI) is at P1.5. There is a directive at the beginning, as a choice between HW and SW-bitbanged "SPI", but I did not really debug the non-HW-SPI part...
  
• my clock was 22.1184MHz. The timer0 can be reloaded in the interrupt (mov TH0,#80h) to achieve the same behaviour at 11.0592MHz.
  
• the "third" mode runs for too long. Needs something like mov AlgoTim,#40h just before the Run3X2 label.
  
  
  
  Enjoy!
  
  Jan Waclawek