4 preamp cards and 4 balanced line drivers using OPA1637.

The Vcom and higher +/-9v rails for OPA1637 buffer are supplied through the stackable headers on the preamp cards. They are 1mm to long so not sure I will be able to squeeze all 8 preamps in there using those. 

The 6mm brass standoffs worked fine for the line drivers and I send the VQ down one line of brass standoffs and it works.