I recently ran a project with a pair of vintage Altec Lansing Valencia 846b and a Lyngdorf TDAi 2170.
I removed the XOs from the speakers and used the XO function in the 2170. I ran the woofers from the 2170's internal amp, then used the analog out from the 2170 into a First Watt J2 to drive the horns. I'd say it was a pretty successful experiment.
I'd used an upmarket passive XO from Great Plains Audio on the Valencias and found the speaker to sound quite rolled-off on the top end and a little muddy in the mid-bass. The experiment with the Lyngdorf lead me to conclude that it isn't the horn/driver that's rolled off, nor is the woofer necessarily muddy sounding, most of the damage was being done by the passive XO.
Of course, the experiment came to fruition when Room Perfect EQ was utilized, which really helped turn this classic horn speaker into something that could compete with a more modern design - detailed, dynamic, good soundstaging ability, respectable imaging, etc.