Originally Posted by BigEinBigD
Bowers and Wilkins 703
A hifi store salesman recommended a parasound 2125 but I don't want to pay 775 just for some more power when I could sell both receivers and get a new more powerful one
Here's the relevant info on the 2125:
125 watts rms per channel into 8Ω, all channels (2) driven
200 watts rms per channel into 4Ω, all channels (2) driven
200 watts rms per channel into 2Ω, all channels (2) driven
Here is the corresponding info for your existing Onkyo tx-nr807
135 watts minimum continuous power per channel, 8 ohm loads, 2 channels driven from 20 Hz to 20 kHz, with a maximum total harmonic distortion of 0.08% (FTC)
145 watts minimum continuous power per channel, 8 ohm loads, 2 channels driven at 1 kHz, with a maximum total harmonic distortion of 0.7% (FTC)
160 watts minimum continuous power per channel, 6 ohm loads, 2 channels driven at 1 kHz, with a maximum total harmonic distortion of 0.1% (FTC)
B&W 703 Info
"The B&W 703's ported enclosure is tuned to approximately 32Hz, and its minimum impedance is 2.8ohms at 100Hz. The impedance remains below 4ohms from about 79Hz to 400Hz—a region of the frequency spectrum that is dense with fundamentals and requires more of an amplifier, over time, than even the deep bass (which makes huge but less constant demands). I would judge this speaker to be moderately difficult to drive. For that reason, I would conservatively rate its nominal impedance at 4ohms. The 703's sensitivity measured about 88dB/2.83V/m."
IMO the relevant comparison would be between the NR807 AVR versus the 2125 with 4 ohm load.
On the test bench a slight edge would go to the Parasound for its 200 wpc spec into a resistive 4 ohm load. While we have no rating for the NR807 at 4 ohms, its 6 ohm performance (160 watts) is probably indicative.
The obvious problem is that 200 watts is only about 1 dB more power than 160 watts. The Parasound's most likely benefit are mental rather than physical. This is a barely audible difference. For reference purposes it takes 10 dB more power (coincidentally 10 dB more power) to create the impression of "twice as loud".
At this point the most satisfying upgrade would probably be a subwoofer. The two 6.5 woofers in the 703 appear to lack punch below 50 Hz. They certainly lack dynamic range. By adding a subwoofer a considerable power load will be taken of off the main channels of the AVR by using a crossover point of 80 Hz or so. I would recommend budgeting the same amount of money or more as you had considered for the power amp upgrade. Subwoofers from Hsu and Rhythmic have a good reputation for price/performance and good general performance.