We have as a OC used, and a number of residents in our complex have used, all succesfully, SLR consulting.
We require (in our by-laws) that the accoustic consultants testing and report be done by a member of the Association of Australian Acoustical Consultants – http://www.aaac.org.au/nsw They are the peak association for these types of consultants and companies. While there are other associations apart from the AAAC, I have heard they are not quite as stringent on their members and the fly by nighters are more likely to either belong to no associations or a less well respected organisation then the AAAC.
We require a report prior to approval for installation, with the consultant assessing the likely impact of the selected underlay and flooring on our types of slabs, then a noise test on site, and then a final report. By keeping to this strict process, we have had no noise complaint issues on floors installed since this was put in place (floors put down before this was put in place have had noise complaints in relation to them in the past few years).