Now I know every piece of audio equipment contributes its own sound signature to a system. And no, I have not demo'd any of the aforementioned options to do an A-B comparison, which is why I am soliciting advice, especially because if I make a purchase, there is likely no avenue to make a return.
There are magazines that will wax poetic about how this amp has a warm or cold sound or hard or soft sound, etc.
However, the goal of any amplifier is to amplify the input without changing that signal. If an amp imparts its own sound signature, that is, by definition,
distortion.
Amplification is a mature technology and should be free of any audible distortion.
Places where amplification may result in an audible difference is when the amp is being pushed beyond its capabilities. Most typically, this would be a situation where either the speakers has abnormally difficult load characteristics (such as impedance drops well below 4 Ohms or very low efficiency) or the amp design incorporates short-cuts (which you will not typically see from a mainstream manufacturer's amplifier).
One concern I do have (but am not sure of) is the Audiosource (and many amps when bridged) only provides specifications for an 8 Ohm load. They do not provide a specification for bridged operation into 4 Ohms. On some amps, running the amp bridged into 4 Ohm loading will cause problems!
Sound and Vision measured the following for your A9's:
L/R Sensitivity:
90.5 dB from 500 Hz to 2 kHz
Impedance reaches a minimum of
4.49 ohms at 67 Hz and a phase angle of –49.39 degrees at 22 Hz.
Read more at
https://www.soundandvision.com/content/polk-rti-a9-speaker-system-ht-labs-measures#uFXmDhF0F4ORWcCq.99
Okay, I found the manual for the Audiosource 300. On page 5, it has the following caution:
NOTE: Only one pair of channels can be bridged together. Do not attempt to bridge both A & B speaker terminals, as this may result in a lower impedance than the amplifier is designed to accommodate, and may damage your amplifier. The minimum impedance for the total load connected to a pair of channels in the bridged mode is 8-ohm.
So, with the Rti A9's, you are operating that amp outside of its intended design parameters!
The good news is 90.5 dB sensitivity means the unbridged 235 Watts per channel into 4Ohm capability of your amp will drive the A9's to ear bleeding levels quite easily.
The bad news is you may have overheated your amp. I would pop the top and look for any discoloration or melting of components. Also check for leakage around the capacitors. Ideally the unit should shut off before any damage occurred. Parts Express should be able to help you with this evaluation, just make sure you speak with a technician familiar with their amps rather than the first CS rep you get on the phone. (sometimes email is the best approach as they will forward it to the right people).
Before you think it was Audiosource that cheaped out on the build of your amp, note that page 6 of the Parasound A23 manual says:
IMPORTANT! - Before trying bridged mono
You should not connect a speaker with an impedance of less than 8 Ohms to the A23 when it is configured for bridged mono operation.
When running in bridged mode, that 4.49 Ohm load becomes 2.25 Ohms and even many very high dollar amps cannot support that low of an impedance for very long!
Bottom line: Your speakers are quite efficient and can be reasonably driven by any typical AVR or amplifier in normal stereo mode. 100 watts is more than enough. Bridged mode increases the wattage available but substantially decreases the amp's ability to deal with high current situations! Just stay away from bridging unless you have a very specific circumstance to recommend it. It is somewhat deceptive that some amp manufacturers throw around their bridged power levels without any qualifiers in their marketing materials.
