SIR-2's a bit pricey, isn't it? (SIR is free but involves a delay that makes it unsuitable for live use - OK for eg playing back a Cubase "sequence".)
If you're not in too much of a hurry, you could wait til Hw has acquired its built-in convolution reverb. Otherwise ...
I wonder whether one of LiquidSonics's products would do. The most basic one is free to try out: if you keep on using it, LiquidSonics wants a donation to their chosen charity. They're all variations on the convolution-reverb theme, including the basic one - so even that one ought to be OK with Jiri's IRs, and might perhaps be all you need.
http://www.liquidsonics.com/software.htmI think there are still a few other cheap/free ones, too.
If I was going to buy a commercial convolution reverb now, and wasn't put off by SIR-2's price, I'd consider paying the extra for the new Quantum Leap "Spaces" (see East West's website), because that comes with ~700 IRs, compared with (what, a dozen, or so?) with SIR-2. However, that wouldn't suit everyone and, for the organ, you'd probably have to like the supplied church/cathedral IRs, because you can only use the supplied ones - not Jiri's or anyone else's. Also, you can't extract the supplied IRs to use with other convolution software (such as will be in Hw).
If you have money to burn (and don't need the heat
), there's always Altiverb, of course.