There is a reason why large competent engineering driven speaker companies do not add really small capacitors across larger ones. I mean Wilson, Magico, Revel, and companies like that.
It is normal to parallel resistors especially if manufacturing volume is low. You can buy a small number of values in larger quantities to create new values as needed. If you can, parallel resistors close to the same value. That reduces the worst case heat in any resistor. If you are using non inductive resistors, even the cheapest ones, inductance will never be an issue at the frequencies we are working at. Follow Erik's advice and get a low temperature coefficient resistor. You can always use a bigger one to prevent self heating. I would not stress too much, the voice coil resistance is probably going to change more than the resistor. Better not to have 2 things changing though.