Having had a bit more time to use the Duende now I can honestly say that I am very impressed with it. It crunches away nicely and has a very solid feel to it sonically.
After reading all the reports about firewire issues I tried maxing out my system to see what happened.
I am able to max out the Duende (28 mono channels and 2 buss comps) AND all my powercore stuff flat out (pci mkI, pci mk II, firewire) AND get the UAD-1 up to around 75% (which seems to be where that particular item stops being happy on my system which is a Dual 2gig AMD 8131 G5) and everything is playing along nicely with no real issues such as the clicks and pops that some people are reporting. I've even got a firewire lacie hard disk daisy chained to the powercore firewire - although it is NOT being used for audio or for any heavy streaming of samples.
Obviously when everything is running at full pelt the taxing on the G5 natively is noticeable - probably around 30% or so... but it's also quite a lot of processing that's going on by then. And it's really quite amazing what running 5 finalizers in serial does to your mix
I strongly suspect that part of why this is working so well is the fact that I am using the G5's own optical audio i/o's, thus not using any third party audio drivers and, perhaps more crucially, not using firewire bandwith for audio i/o.
With all pci slots taken up in my G5 a firewire pci card wasn't really an option, so it's no less than GREAT that it works without one. The Magma route is one I'm not really prepared to go down at this junction...