The answer to your question depends on what sort of data you want to
send between the 2 01V's. The "to host" connection will allow you to
send basic control information like fader mode from one 01V to another,
using what appears to be a standard serial cable. This provides
similar functionality to connecting the 2 O1V's via MIDI. If you want
to send audio between 01V's, you will need one of the expansion cards
(ADAT, AES/EBU, etc.) unless the 4 analog omni outs are sufficient.

Take a look at pages 214 & 239-240 of the manual.
http://www2.yamaha.co.jp/manual/pdf/...ixers/01VE.pdf

Travis Garrison