Re: Upgrade the tremolo on RG1570
You can't really replace an Edge Pro with another Ibanez trem without seriously modifying the guitar, but I think an Original Floyd Rose will fit, not done it myself though so might wanna confirm that.
That said, as others mentioned the Edge Pro is one of the best trem systems money can buy, replace the posts with the locking ones (if you feel the need) and it's effectively a more modern one than what Ibanez currently use on their high end guitars. Ibanez went back to the past to the Original Edge and Lo-Pro Edge due to their popularity, but barring the locking studs (which you can upgrade) the Edge Pro is just as good, better if you like the modern features.
What's wrong with your current trem?