Hi again, All Bang & Olufsen "Beolab" and "Beosound" loudspeakers are "digital" loudspeakers; meaning that any signal that comes in is converted to a digital signal for all processing, and then converted back to analogue signals which are sent to the amplifiers for the individual drivers. This is true whether the device has a digital input, an analogue input, or no input (meaning it only has "internal" sources). In some cases, the Power Link input and the RCA (Line / Aux) input are essentially identical with respect to technical sound performance. In some cases, there is a difference in the maximum allowable input level (and therefore the sensitivity of the device: a measure of output level as a function of input level). In the specific cases of Beolab 5, Beolab 50 and Beolab 90, the  input sensitivity of the line inputs are user-adjustable. IF your source / preamp has a high-enough maximum output, then it can overload the line input of the loudspeaker - but this is something that has to be specifically determined for the output and the input of the products in question. Be careful making conclusions when comparing things like an analogue connection to a wireless digital connection. There are so many individual components in each of those two signal paths that may have an effect on sound "quality" that there's no real way to know why they may be different, if they are. You certainly cannot conclude that "analogue wired is better/worse than digital/Airplay/Chromecast/Whatever" without doing an extensive amount of testing, including being able to measure the signals at points in the chain within (not between) devices. In other words, it's not possible for a normal person without a lot of test gear to do this and arrive at a reliable conclusion. In addition, an overnight firmware update may make all of your conclusions irrelevant. Finally, be careful to not confuse the terms DAC (Digital-to-Analogue Converter) with ADC (Analogue-to-Digital Converter), which appears to be happening above... :-)