its done all the time but before i put 6 eight inchers i would just get two 12's but i guess you have ur reasons for choosing 8's so tell us what eights they are an what type of Voice coils they have an we will let you know what to do or what amp to get if you dont already have a amp
Unless you can't do simple math, putting 3 speakers on one channel will not harm anything. You must make sure that the impedence shown by the circuit is greater than the lowest stable impedence of the amplifier.
I've put 8 speakers, in parallel (4ohm DVC in series), on one circuit and it has run fine.
Well the reason I am using 6 8s is i am putting them under a friends rear seat in his extended cab truck ... the box is a lot smaller than the one i would have to use for 12s. His main conscern is space ... he wants to take up as little as possible with still getting a lot of punch.
The speakers are Rockford Fosgate Punch stage 1 4-ohm , 50-150 RMS, SVC, Peak 300w