Would be surprised if it makes a difference. Most of the time this is about low passing the signal send to the sub not high passing the signal send to the speakers. But you can try. Run a sine sweep e.g. 30-200 Hz with the low pass set to 120 and again with the low pass set to 40. If it makes a difference, stick to 40. If not, this setting is irrelevant as you don't use a sub.