All-pass filter usage in automotive room correction This may not be the right place to ask this question but I'll give it a shot anyways. Maybe someone here is an audiophile. 

I'm using a DSP called Audison Bit One HD which uses FIR filters for crossover and EQ. They recently included all-pass filters which allows me to adjust the phase of the crossover point. I'm wondering if anyone here knows how this will benefit for room correction. 

I know what an all-pass filter does but I'm not sure how it could be useful with FIR filters which is a linear phase filter. Why would I want to adjust the phase of the crossover point for?

The manufacturer is no help.
Allpass filters are very helpful in automotive mainly for getting the imaging dialed in. You often need to time align the contributions of different driver groups (left, center , right) at a specific listening position. Due to the complicated acoustics of the cabin. the delays are often dependent on frequency and so all passes can be very helpful in correcting this.
Allpasses in cross overs are typically not that useful, since the range of overlapping frequencies is pretty narrow and you can typically get by with a single delay