I own the A3 MF amp.85 watts/8 ohms,170/4 ohms.I don't think you will need the additional power of the A300 with the efficiency of the Klipsch,and you will save $500.
I have several MF amps/integrateds but am not familiar with
Klipsch ref 3 speaker, but if you have sub woofer that does not have its own built in amp, you may want to go with A300
for 150w to control sub. Both A3 and A300 have preamp out
RCAs to allow easy bi-amping with another MF power amp.
If sub has own amp, and klipsch are just stand mounted monitors, A3 should do the job.