GOOD QUESTION!!! I have 2 Crown XTI 2000 amps and 3 turbo sound subs. I want to overlap equipment but not too much, ya know for back up purposes.
Small system = 2 EV ELX112P
Back up = 2 EV ELX112 w/Crown xti 2000
Med-Large System = 2 EV ELX112P and Crown xti 2000 w/1 turbo sound 18 or 2 turbo sound 18s
Back up = 2 EV ELX 112 w/crown xti 2000 and Crown xti 2000 w/1 turbo sound 18 or 2 Turbo Sound 18s
Large-Huge System = 2 EV ELX112P and 2 EV ELX112 w/Crown xti 2000; 2 CW C36 earthquakes on 1 Crown XTI 2000 bridged Mono @ 4ohms
No Back Up =
I may get another amp, say a Crown XTI 1000 as the amp for the passive 112s, but I don't want to be like my friend who has great equipment but about 8-10 amps and 10-12 speakers/subs. I need all of my equipment to do double duty when necessary AND be backups for some systems (total of 7 speakers/subs as I will get rid of 2 subs and my EON G2s). If I got the XTI 1000 I could use both of my 2000s to power each Earthquake. If one of them gave out on me I could get by with 1 but would rather have 2.
For me the ROI and cost-benefit ratio have to be right otherwise it makes no sense to have so many speakers/subs unless I plan to do those types of shows. The largest shows for me are my proms, which get up to about 700 people max.