Not that I know of. They come with no amps (preamp/processor) or with all the amps (A/V receiver). Of course, you do not have to use all the amps.
It seems the cheapest Marantz receiver (NR1501) doesn't have pre-out. What other cheap options are there that have pre-out?
Also, it seems most receivers are 7-channel, which seems wasteful since I will only use 3 of the channels. Is it common to have bridge a bridge mode, so that two or more channels can be combined?
I really like the Onkyo receivers. Yes, any of the current models will be 7 channel. Some will have bi-amp option that will allow you to bi-amp a pair of L/R front speakers if the speakers have bi-wire/bi-amp inputs.
Check the various receiver manufacturer's websites or a large vendor site like J&R. You should be able to easily find receivers that have pre-outs and have bi-amping capability.