Yes, a preamp will add some distortion or cause the signal to "lose" something. But like any other active component the power supply, regulation and output devices will determine everything. A top-notch preamp will overcome any loss that occurs with adding another compnent to the chain. The quality of the output of a good preamp in terms of dymanics, frequency response and voltage swing will be much better in many cases than the output of cdp's all because good preamps have better power supplies.
With respect to impedance matching, the lower the output impedance of the preamp means that more voltage is transferred to the amp. This is because power is eaten by resistance - and the more output resistance a preamp has, the more power it consumes from the signal, leaving less voltage at the amp. The amp is now forced to swing a higher voltage difference in a fininte amount of time making things more complicated and affecting the sound quality. So a preamp with a lower output impedance than a cdp is an overall plus - even though there is a slight loss in signal transfer.
Bottom line - good active preamps will be a plus because if they weren't, then who would buy them? We would all have passives or cdp's with volume control.
With respect to impedance matching, the lower the output impedance of the preamp means that more voltage is transferred to the amp. This is because power is eaten by resistance - and the more output resistance a preamp has, the more power it consumes from the signal, leaving less voltage at the amp. The amp is now forced to swing a higher voltage difference in a fininte amount of time making things more complicated and affecting the sound quality. So a preamp with a lower output impedance than a cdp is an overall plus - even though there is a slight loss in signal transfer.
Bottom line - good active preamps will be a plus because if they weren't, then who would buy them? We would all have passives or cdp's with volume control.