I would change the amp first, you might not need to change the speakers. Amps like the one I use, Musical Fidelity NuVista M3, are available at around $2400 used on Audiogon and would completely transform your system. They are rated at 275 watts at 8 ohms but can deliver far more power at lower impedance's, which they will see driving both pairs of your speakers. The bass will improve beyond your wildest hopes and the top will also be better. Try to borrow a good modern solid state amp and see the difference it makes before changing speakers.