Sounds as though you have a nice system as it is.
The bass effect with the BL 4000 is strong, and many on this forum have noted before that the BL 4000 is one of the more underated speakers in the BL line. I have used a BS 3200, a Plasma surround, and ML link for 8 years now using the BL 4000 as front speakers ( on an old Danish Teak cabinet supporting the Plasma ) with BL 6000 as rear sound source. Sat TV, DVD, and music sources are all excellent in fidelity. My wife and I watched one of the " Foyle's War " DVDs last night, and the surround sound was clear, crisp, and remarkable.
No complaints, not even from the neighbors.