how to safely increase the distance between ws2811 chips
My guess is that limitation is due to a crappy output driver.  So you could use a line driver to drive the wire to the first chip.  Basically, all you need is an op amp with enough 'oomph' to drive the capacitance of the line.  Alternatively, a differential driver is a good idea.  I would suggest using an RS485 or RS422 to TTL translator chip.  These are pretty easy to come by and will convert a single-ended signal into a differential signal with enough drive strength to drive quite a bit of cable.  An RS422 chip might be ideal; it has an independent transmitter and receiver.  You can put one of those on on each string of WS2811 to convert both the input and output signals for daisy-chaining.