K-horns are just about the most efficient loudspeaker on the planet. You can drive them with one of those under 10 watts single ended tube amps. Back in the late 50's Klipsch decided that a center channel was a good idea, which is where people started using the Heresy, La Scala or Cornwall. Some of the receivers, integrated amps and preamps of the day had line-level center channel outputs. You'd feed that to a mono power amp to drive your center channel loudspeaker.
$1500 will certainly get you some decent solid state gear though it's going to be hard to find a solid state piece with a mono output for center channel. You could look to score something like a Fischer integrated tube amp or 500C receiver (they'll have a mono output) and add a mono tube amp. You could probably do that within your $1500 budget.
You could build a preamp equal to anything sold here on Audiogon from Glass-Ware Audio for about $500 in parts. But you'd have to know what you were doing or know someone who can coach you.
But by all means, remember that you don't need more than about 3 watts to drive K-horns. 3 watts into K-horns is like 200 watts into most any other loudspeaker. Efficient, remember?