Hello ecruz,
It depends on the speakers.
Horn speakers may or may not be designed specifically to work well with high output impedance specialty tube amps. If they are, that doesn't necessarily mean they won't work well with NuForce amps - it depends on the impedance curve and/or the "voicing" of the speakers.
About a year ago I designed two waveguide speakers giving high priority to compatibilty with high-output-impedance tube amps. To make sure I wasn't painting myself into a corner, I used a NuForce IA-7 as a test reference. What I found was that the impedance curve of the loudspeaker had to be kept very smooth to avoid a tonal balance shift when going from the high output impedance tube amp to the NuForce amp. For a while I was afraid that I'd have to offer two different versions of the crossover, but by keeping the impedance at 10 ohms plus or minus 20% the tonal balance shift is just barely audible and imho insignificant.
On the other hand, if the hornspeakers (or any other speakers for that matter) have significant peaks and valleys in their impedance curve (don't worry about the bass tuning impedance peaks for now), then their tonal balance will change significantly according to amplifier type. In that case, you need to call the speaker manufacturer and see what he says. Typical loudspeaker impedance curves can give you 3 dB or more variation in the midrange depending on the output impedance of the amplifier.
Bass response is affected by the amplifier's output impedance, and you might need to adjust the bass tuning if the speaker was tuned for a high-output-impedance tube amp.
I use my IA-7 regularly on my waveguide speakers, and typically use a bit shorter port (higher tuning frequency) than when I use a high-output-impedance tube amp.
As far as NuForce amps being overkill power-wise, I have a friend who uses 100 watt per channel Class A solid state amps on 107 dB efficient hornspeakers. And no, he doesn't listen loud - he just really really hates anything remotely approaching clipping.
Duke
