Mike:
I love Altiverb. It is IR based, but you can vary many parameters,set EQ, change room size, change reverb time. position the sound source. IR samples are frequently added, but it already comes with IR samples of many famous halls - e.g. large halls Amesterdam's Concertgebouw, Berlin's Philharmonie, Vienna's Konzerthaus, Sydney Opera House, Disney Hall (L.A.), etc. smaller halls like the Mozart Hall (Vienna) Schubert Hall (Vienna), Kammermusiksaal (Berlin), cathedrals, churches, sound stages, clubs, etc. etc.. Samples are from multiple positions . eg. 6 meters, 12, meters, 20 meters, 28 meters, etc. depending on the hall. Altiverb has a reputation for being CPU hungry but, according the manufacturer, Altiverb 5 & 6 are less so than previous versions. On my system, using multiple instances of Altiverb, this has not, so far, been a problem. As Steve Martin sugests, download the demo and see if you like it...