I would be one Audiogon member to disagree... introducing a crossover into the signal path might actually affect the resolution and the magic of the SF Concertos. Are you unhappy with the current sound?
If you have bass problems, I would first recommend investing in a sound level meter and a test cd with specified bass frequencies to see/measure if you have excessive bass or bass suck-out at certain bandwiths, and play with placement of- and the crossover setting of the REL. You can pick up a Radioshack SL meter for about $50 and a Rives Test CD 2 for $24 that is designed to be used with the Radioshack meter.
If you really have problems that require a crossover, I would look at the new equalizer from Velodyne, but that would be a considerably more investment.
If you have bass problems, I would first recommend investing in a sound level meter and a test cd with specified bass frequencies to see/measure if you have excessive bass or bass suck-out at certain bandwiths, and play with placement of- and the crossover setting of the REL. You can pick up a Radioshack SL meter for about $50 and a Rives Test CD 2 for $24 that is designed to be used with the Radioshack meter.
If you really have problems that require a crossover, I would look at the new equalizer from Velodyne, but that would be a considerably more investment.