A passive preamp does not have any active amplifiers in it. It may be an input selector wired to a passive volume control or stepped attenuator. It can also have transformers in it that will add some gain to the signal passively and isolate the sources from the amp. There are different opinions about whether it is better than an active preamp. It basically depends on the system (input levels, amp and speaker sensitivity) whether it will play loud enough without the additional gain that an active preamp will add. Most CD players will put out max 2v. A preamp can put out as much as 10-20 times that much on peaks so can be more dynamic in driving your power amp. The interconnect cables become much more important in a fully passive...