Are SOS structures better for linear phase FIR filters? I've seen many discussions suggesting that SOS's are often/usually the preferred structure for fixed point hardware filter implementations, since they preserve conjugate pairs, etc., but I've never seen any specific arguments explaining why they are better for FIR filters.

Do these advantages still apply for direct form, linear phase FIR filters which allow the number of multipliers to be reduced by a factor of 2?

Finally, are there any good resources discussing these trade-offs?  I'm trying to implement fairly long FIR filters with small multipliers, i.e. 40+ taps with 8-10b coefficients, and am looking for resources that might shorten this effort.
well, i see little value in factoring an FIR into quadratics and implementing them in cascade.  it won't be computationally cheaper and it's not better from a quantization noise POV if your FIR has access to an accumulator that is double width.  

perhaps it will help with limiting coefficient range so that it's less likely that you have non-zero coefficients (at the tails of the FIR) with values of, say, $10^{-8}$ the size of other coefficients (in the middle).  there are other, more efficient ways of dealing with that problem (like computing the FIR from the outside in, doing the tails first and the middle last).