Expanding a 2-channel system to surround

I would look at receivers.

marantz avrs are a good bet for your application--you can configure to use your krell to power the fronts and use the avr for center and rear.

As Theo and Loomis said, look at receivers. Personally I like the Onkyos. Use the processor functions of the receiver and use 3 channels of amplification from the receiver. I set up a similar setup of several different occasions with good results.

Enjoy,

TIC

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?

Ahochan,

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.

Enjoy,

TIC