It's just an amplifier, not a receiver. You still need something to do the signal processing. It's not an "upgrade" from a receiver because it doesn't perform the preamp processing of a receiver. Many people use their receiver as a pre-pro, but the receiver needs preamp outputs for that and the Pio 520 doesn't have any.
The Pioneer doesn't have a great amp section, but it's decent. Unless you listen loud, it's probably entirely adequate. In order to upgrade the amp, you'd need to either:
1) Replace the Pioneer with a receiver that has a better amp, or
2) Replace the pioneer with a pre-pro or a receiver that has preamp outputs, then add an external amp.
$1000 seems like a lot of money for a 2-channel 90 watt amp. I dunno if they ship to Australia, but Emotiva sells the UPA-2, a 125 watt 2-channel amp, for $300. You can also get a pro audio amp that'll do over 300 watts per channel for around the same price.