The would only be providing clock & data to one chip, that chip buffers the 2 lines and passes it along, yes?So power them from their own 5V source, connect all the grounds together.
At 5V, the WS2801 needs 0.8*Vcc = 4V minimum for Vih.Run the signal lines thru a TXB0102 buffer. Only micro-amps of output current are needed.Or, run the WS2801 from an external 3.3V. Still just need micro-amps of output current for the control pins.
Ok, it looks like the WS2811 does NOT respond to signals at 3.3v. So, I'm investing in some 74LVC245 ICs (https://www.adafruit.com/products/735) to convert my 3.3v to 5v.