do you have the speaker switch on, on the receiver? the amplifier obviously works because you heard the headphone fine. 90% of the time, if the transistors of the receiver is bad, you will get distorted sound or no sound out of the headphone jack.
you will get sound out of the subwoofer if it works. it will be bass only if it's crossover already or it will be bass with ****ty sounding midrange if it's not crossovered.
take a 1.5 volt AA or AAA battery to the positive and negative terminal of your speakers to see if it will work. it will pop out if it works.
that said, you might have a stuck speaker output relay on your receiver
what kind of receiver is it?