The file sizes depend on the number of channels (3, 4, 5, 5.1) and the resolution (DSD64, 128, 256). When you compare a DSD64 Multichannel file vs. a DSD256 Stereo file, they're very comparable in size.
I have ripped a large number of mch DSD64 files from SACD's. They are typically around 5GB up to 7GB. My only stereo DSD256 is 5GB for a 40 minute album. So they are very similar in size. So my 400 mch albums take about 2.5 TB (x 4 including 3 backups) = 10 TB. I have two different NAS systems and 2 external 4TB drive sets for the files and their back ups. I also save the original .iso files and have ripped those into stereo files, too. So fortunately, storage is dirt cheap and getting cheaper than dirt.
Larry