* Eric, your Boston Acoustics HD8 have an 8" woofer, right?
Only for these two, try the crossover at 60hz, just to check if you like it more.
If not, because these, if I remember, are very old speakers, I will recommend that you shop for new speakers. The time has come Eric, and it's a very important step, the most important actually.
Eric, sorry if my memory is short right now on that one, but I believe your X-overs are at 80hz and 100hz, right?
NO, don't lower them, only the two front mains (try 60hz).
You need to make your speaker's stands heavier and stronger. Are they wood ones or metal ones? Can you add Shot Lead in the tubings if they are?
If not, you have or to use Blu-tack to the top plate, so your speakers anchor better withy the top surface.
Also if your room is carpeted, I highly recommend spikes under the stands, also for better anchoring.
Here's a tip: On the bottom plate, add some weights, heavy bricks or lifting weights, or marble rocks, or anything heavy. Even on top of your speakers, you add weights too. The heavier the stands with the speakers, the better the bass definition.
Cheers,
Bob