Given the BIP II with 1" shroud box, why not simply block off the area for one fan and use a single 120x38mm fan to pull? Contra-wise, that shroud is simply adding plenum as the BI rads are already shrouded. I've tried extra plenum on BIPs (Is not IIs) and have seen a slight improvement when adding it on the push side, but no improvement when used on the pull side - so you could likely ditch the add'l shroud and get a little extra space, which might reduce exhaust turbulence.
If you are looking to reduce noise, you don't really need 38mm thick axial fans to pull through a BIP. I've had best luck with Nexos 120x25mm fans. I've recently found look-alikes (from the same fan manufacturer) at
isellsurplus .
A second 120mm Panaflo 'L' might quiet things as well - although the Panaflos (the ebm/papsts too, come to think of it) do not like being speed controlled with PWM. Are you getting a "ticking" noise? Try speed controlling with simple resistance.