Hi Fred, presume this is your 1st Bass then?
I'm a bit spoilt for choice at the moment as after playing my recently acquired Ric 4003 more than the others that highlighted just how weak and whimpish these 5 stringer PUP's are. Same goes for my J Bass and just ordered the highest grade Entwistles for that axe on Sunday night and it will end up being the best $80 bucks spent to improve it's sound.
The stock Chinese units that come with all these kits tone wise usually don't sound too bad but their output is way lower, and when on the Ric if I was ever gigging with them as backups it would require me to continually adjust the volume after each axe swap. Onstage Bass volume is hard to control at the best of times and I can only imagine things getting way too loud as the night grows longer.
Cheapest solutions for your IB5 might be.....do nothing.....buy the 2nd hand Bartolinis on eBay for AUD $150 plus postage....or buy the cheapest Seymour Duncans on US Amazon site for USD $125 which works out at about AUD $175. PM me if you want help finding the 2nd hand Bartolinis on eBay.
At the end of the day tend to find if I am not totally happy with one of my axes it rarely comes out of it's case for a play which is a shame as they are built to be played rather than gathering dust as a collectible or piece of furniture or artwork. If you chose to upgrade I reckon you will not regret it as even the cheapest option will make a significant difference to output, just not so sure on the tone aspect as that tends to come more with the higher end stuff that costs just a little bit more. At times like this you hate the falling AUD against USD & GBP.