Pre-outs bypass the internal amp of the receiver allowing you to use an external amp to drive speakers. Receivers are notoriously over rated when it comes to output power. Typically a 100 watt receiver driving 5 speakers actually feeds the speakers 50 watts each or even less. They are rated driving a sine wave at a specific frequency through one channel for the highest rating. You do not have to purchase a receiver, you can purchase a pre-pro and separate amp. Emotiva will sell you a UMC-200 and a UPA-500 for about $950 but you would also need RCA's to connect them. Yes this is more than a receiver however their amp is rated at 80 watts x five all channels driven. If a receiver is what you are looking for, and you want the option to later add more amplification, then look at receivers that have the pre-amp output feature. All of the big Japanese companies have models with and without them. Sony, Denon, Yamaha, just to name a few.
