You don't say what sub you are currently using. However, by normal standards you have the crossover too low. 80Hz is the THX recommended crossover frequency for all but the very largest floor standing speakers.

The general idea is to give the frequencies to the speaker that reproduces them with the lowest distortion and the least strain on the amp.

Most quality subs have no problem reproducing up to 80Hz and higher with their drivers and dedicated amps. You say your Yamaha bookshelf speakers are rated to down to 45 Hz. However, that spec is meanlingless without a reference level such as "-3dB's." I could not find any info on that model number. Is it from a HTIB system by any chance?

Mainy people think that you should crossover the sub at the lowest frequency response level of the main speakers. That is simple not true. The crossover should be made based on many factors including if the main speaker or the sub reproduce that particular frequency the best. For example, lets say your sub plays up to 125Hz at -3dB's and you speaker play down to 40Hz at -3dB's. 40 Hz is not the correct crossover frequency (neither is 125Hz). 80Hz is a good compromise and also frequently commonly chosen for good reasons. Most quality subs reproduce this frequency better than the speakers they are mated with. At this frequency and below, most people cannot audibly determine the location of the sub (thus the sub can be located other than at the front of the room). Another benefit is that it relieves the amp in your receiver from powering the lower frequencies which place a much harder task on the amp.

The crossover frequency for your new Energy speakers would depend on the particular models you ordered. Most likely it would be 80 or higher. For any crossover higher than 80Hz you might be able to determine the location of the sub and would want it at the front of the room along with your main speakers.

RR6