Why is this the case?To illustrate this, lets follow the signal on it's path from the CD player through to the loudspeaker system, and ultimately to the human aural system. We will assume a reasonably respectable amplifier with less than 0,01% total harmonic and less than 0.01% intermodulation distortion. The voltage level of the audio signal from the CD player appears at the input leg of the first capacitor in the amplifier chain as several hundred millivolts rms. Lets say, 440mV r.m.s., the old domestic line level. (Nowadays its usually a lot higher at around 2V r.m.s.) This originated in a recording studio from electrical signals fed to a mixer desk via a set of microphones. Already the signal has passed through scores of capacitors. The composite signal is recorded onto a master tape or disc and then stamped onto your CD as a series of miniscule digitally encoded bumps and troughs. The undulations are read by a laser and converted from digital form to analogue form as a varying voltage. At the input of the amplifier , the harmonic and intermodulation distortion level in the source music is well above the distortion and background noise level of the amplifier. Now let us consider the distortion caused by a 'non-audiophile quality, capacitor' in the signal chain. The level of the capacitor distortion components relative to the source distortion is hundreds of times lower. In fact, in our decent amplifier, it is well below the noise floor. You couldn't possibly hear it. Looked at another way. If the total harmonic distortion in the signal is 3% (a very conservative figure) and the total harmonic distortion (THD) of the amplifier is a mere 0.01%, (which includes the much lower distortions from the capacitor), it doesn't take a genius to see that mucking about changing capacitors for the sake of it, won't make any audible difference. Now let's follow the signal out of the amplifier:The signal travels from the amplifier as an amplified voltage and current through the speaker cable to the loudspeaker's speech coil. This causes a changing magnetic flux in the coil which interacts with the fixed flux in the gap between the coil and speaker magnet to create cone motion. This in turn creates sound pressure waves. Here the total harmonic and intermodulation distortion leaps up even further. A figure of 5% would again be very conservative. The non-linearities inherent in the loudspeaker to human aural system, makes any capacitor distortion look like a nit on a gnat's eye lash. First in the loudspeaker, the non-linear conversion of changing current to changing magnetic flux adds appreciable levels of distortion. Then the non-linear conversion of magnetic force to motion in the cone adds even more. The conversion of cone motion to sound pressure waves adds more still. Finally your own set of aural receptors, non linearly convert the sound pressure waves into electrical nerve impulses in the brain. You own ears add considerably more distortion than the difference between two capacitor types.A much more serious distortion, more like an interference, occurs in some male brains. This blurs the original thought of inserting a CD, relaxing, and listening to the music. Instead thoughts of that nasty non-oil filled capacitor, loom in the brain. The truth is, the distortion, compression and background noise of most CD & Vinyl recordings plus the non-linear distortions in the loudspeaker-aural system, has hundreds of times greater effect on the original sound than the effect of changing a resistor or capacitor to an audiophile type. That non-faulty component is innocent ! Leave it alone (unless of course its faulty) and enjoy the music! In some cases, changing to audiophile capacitors can actually decrease performance see polypropylene versus oil filled blog polyprop V OF. When we service a typical vintage amplifier we often replace all the electrolytic capacitors and several resistors, not because they are 'better' so called, 'audio quality types' types but because many have deteriorated. i.e., either one or more of , low value, o/c, s/c, leaky, high ESR etc, etc.We insist on using high quality electronic components in all our service work for long term reliability.