My Coincidents are at a 97 db sensitivity, so I don’t think that is inefficient, but what do I know. Seriously, using an 8 Ohm amp on these 14 Ohm speakers will cause what kinds of problems?Yes- at that impedance 97 dB would be a high sensitivity. In practice though it appears that the speaker is more like about 94. Using the 8 ohm tap will be no worries.
That amp would sound fine, but if you plan to fill 1000 sq feet(!) you'll need considerably more power unless you will be fairly close to the system.