The use of "fill" indicates that you may want a much higher sound level than is used while at the computer. It also may help to explain why three Audiobyte drivers have gone down. What did Axiom suggest was the problem(and were they mid-woofers, tweeters or both?)? You may have simply been playing them at a level well beyond what the amplifier(intended for typical computer speaker use)could handle without clipping and damaging the drivers.
If the lower sound level which is safe isn't adequate for all your uses, then yes, a bigger and more powerful setup would be needed. I'd strongly suggest a multi-channel HT receiver even if you're only considering 2.1 use now. The bass management to cross over the sub and speakers(which almost no 2-channel receivers have)is a substantial plus and the economies in producing these units in quantity result in getting more for a similar amount of money compared to stereo units.
I've visited Sydney, but know almost nothing about the Australian audio equipment market. I took a look at a Sydney dealer here
for the sort of unit I might suggest, but was appalled at the price, which at about $460 USD was about twice what would be paid in the U.S. Possibly shipping and other charges involved in your buying from the U.S. would almost wipe out any savings. In any case, I'd suggest an Onkyo or Denon 5.1 model in the 80 watt or above class, or if you get just a stereo unit, the HK-3390 would be suitable.