How to amplify four 'front- speakers

Newbie here. I have an old Sony DA3ES Receiver driving an equally old pair of B&W DM640s with B&W 303s for side-positioned surrounds. The receiver has connections for only two 'front' or 'main' speakers so the 303s are hooked up as surrounds. Is there a way to get the signal going to the mains to also travel to the 303s?

Not safely. The 640's specs show that they are a 4 ohm load, while the 303's are a 8 ohm load. Doing the math shows that your Sony receiver would 'see' a combined 2.7 ohm load, which it is probably not strong enough to drive.

In fact it would take one amp with a VERY stiff power supply to drive both those speakers at the same time, an amp that is stable down below 2 ohms.

You could use an Adcom GFS3 or a Niles speaker switcher box.

http://www.ebay.com/sch/i.html?_trksid=p3984.m570.l1313.TR0.TRC0&_nkw=adcom+gfs3&_sacat=0&_from=R40

Thanks for your help, Mofimadness. Would the Adcom speaker box be able to differentiate between the 4 ohm and 8 ohm speakers and drive all four properly, or do all speakers connected to it need to be the same impedance? I love my 604s but finding two more is no easy task.

The Adcom GFS3 has a "protection" button on the front. When in use, it keeps the impedance at around 6-8 ohms, so the amplifier is protected.

I have owned a few of these and they work very well. There is also a GFS6 that does up to 6 pairs of speakers. The GFS3 does up to 3 pairs of speakers.

I have a pdf of the owner's manual I can send you, if you would like.

Thanks again...this looks to be the way to go. I was able to download the needed owners manual but I appreciate the offer!

Right now, with the 4 ohm 604s hooked up as the mains/fronts and the 8 ohm 303s as the surrounds, the sound is good. Having said that, would I expect to get better performance using the Adcom box where the main signal will go to all four speakers instead of just a surround signal going to the 303s?

I think you need a multi-channel (4?) amp. There's no way that Sony is driving the B&Ws properly. Ignore the supposed wattage specs of the receiver. The Adcom speaker switch box is OK, but I'm not big on Adcom amps.

I agree the Adcom will work, however you must keep the "protection" on when using both pairs of speakers, or the load on the amp will be 2.7 ohms as mentioned in the first response. This could eventually result in damage to the Sony. Here is another solution,

http://www.monoprice.com/products/product.asp?c_id=109&cp_id=10903&cs_id=1090307&p_id=8231&seq=1&format=2#description

This will provide proper impedance matching, and also give you volume controls to balance between the two pairs of speakers. Once the desired balance is achieved, then just use the main volume on the Sony.

Even with your current setup, the impedance selector switch on the back of the Sony should be set to 4 ohms. Sony must be turned off when changing switch position.

Well, I grabbed an Adcom GFS6 from eBay so will see how that works. I got the 6 instead of the 3 as i want to send music into a number of different rooms.

I'll report back on how this works...and thanks for all the helpful replies!