Actually, competent UPS manufacturers give you the capabily of paralleling more than two UPS modules.
I don't have a pricelist handy, but if you really need N+1 redundancy, looks at two 80kVA or three 40kVA modules.
Don't forget a method of completely manually bypassing your UPSs, if there is...
I just joined today, but wanted to add my two cents.
I have been troubleshooting power quality porblems for 27 years. We first used the BMI PQ monitors and then switched to the RPM 1650s. RPM was bought by Fluke and their latest version is the 1750s and 1760s. We still like the 1650s best...