I've also heard about similar issues with the Extremis. The Ascendant Audio driver is 88dB 1W/1M - and only $35. I just ran a model on this driver in the same size enclosure with same tuning frequency as the RS180-8 and this driver has slightly more extension. It also handles a bit more power.I was hoping that someone out there has heard the driver. From what I've read, it has a pretty good sound - but I've heard nothing about anyone using them in an array. I know that the inductance is .05mH - so it has potential for greatness from that standpoint.
Thinking about the benefits that an array offers - the extra excursion might not be used. But it is there if you need it (eight of them would have a maximum potential of around 126dB - what would you possibly use for a tweeter with THAT?)
On the subject of tweeter - generally regarded as 'best bang for the buck' (PT2?)? How about the 'upgrade' from there (NeoCD2.0?)?