4 ohm speaker to 8 ohm reciver

Nothing bad will happen! All present day receivers are well-designed and capable of handling 4 ohm speakers.

+1 roberjerman

You should look up the wpc on the Arcam for a 4 ohm load vs. the 8 ohm rating. Should be 1.5x, better if 2x. Also look up the impedance for your speakers across the frequency range. Hopfully impedance doesn't drop below 3ohms amywhere.

Otherwise, and given this is an Arcam receiver, if at maximum use volume the speakers don't sound stressed the compatibility should fine. 

Hi,

Did you say you were bi amping the speakers with secondary channels out of the receiver??

There should be no problem.

I’ve had a few different receivers, but no Arcam, and on many of them on their rear face plate is a switch which changes the transformers output taps from 4 – 6 – 8 ohms. Look for that. It could be too if a very late model unit, the switching is in the settings menu, or the receiver is simply capable of driving a variety of speaker IMPs due to a good transformer in its construction.

Given your new SF speakers, start looking for an amp to add to the receiver which will drive and make them sound much better.

Good luck.