Welcome to Audioholics!
You are confused about those speaker power ratings. Klipsch gives two numbers,
Sensitivity and
Power Handling among other speaker ratings. Sensitivity is a measure of how loud the speaker is when fed a 1 Watt signal with a measuring microphone 1 meter away. And Power Handling is how much power the speaker can handle without overheating and failing. Don't confuse power handling with power requirement – they are not at all the same.
The
RP-250C speaker is rated with a Sensitivity of 96 dB, and rated as handling 150W continuous or 600W power for brief peaks. 96 dB is very loud, even if Klipsch is exaggerating that value. You'll probably sit farther away than 1 meter, but a small amount of continuous power, under 10 watts, will drive these speakers quite loud.
The
R-28F speakers have a sensitivity of 98 dB and power handling of 150W / 600W. These speakers will be a bit louder than your center, but otherwise, the same comments go for these speakers as for the center speaker.
Your
Yamaha TSR-7850 is rated (as you mentioned above) at 110 W (8 ohms, 0.9% THD) if its measured at a single frequency of 1 kHz. Just below that on Yamaha's spec page is the so-called FTC rating (see below) of 95 W (8 ohms, 0.06% THD) if its measured over the full audio range of 20-20,000 Hz. Let's use that second rating of 95 Watts.
Your AVR should be easily able to drive all your speakers at reasonable listening levels, without clipping. All three of those Klipsch speakers are very sensitive and don't require much power to drive them quite loud. Yes, if you turn your AVR up past 11, you might reach the point where the receiver cannot provide more power, and it clips. But otherwise your fears in Question 1 don't apply. Question 2: Don't waste your money. First try your AVR alone. I'd be very surprised if you find it inadequate.
FYI:
That 2nd power rating is called the FTC or continuous rating because the Federal Trade Commission required all audio amps and receivers be rated like that. This way when you're shopping, it's much easier to compare the power of different receivers. Most people, if they want to cite just one power rating use the more conservative FTC rating.
Also note the two different total harmonic distortion (THD) values. The higher power of 110W produces 15 times more THD (0.9%) than with 95W (0.06%). It's debatable whether we really hear THD below 1%, but the lower the THD the better. Another reason to use the more conservative FTC rating.
