I agree with Dkarmeli. You can improve the sound of your Boleros by moving the drivers into new (larger) cabinets and rebuilding or replacing the xovers. But at that point they will be something different and not Bolero speakers.
Getting more bass from Altec Bolero 890c Speakers
I would like to increase the bass response (dig deeper) of my Altec Bolero 890c's speakers. They are rated at 50 watts, and according to the Back-to-Basics Audio by Julian Nathan - simply adding more dampening material would do the trick and would also increase the power handling of the speaker. Is this true? I also read in another thread here, about place a large baffle around loudspeaker, and that Altec did this on many theater models. Has anyone ever tried this with their Boleros with positive results?