I'm currently working ITB for Drums, Piano, Strings, Horn Section, Synths. Save for synths, they are all high RAM usage. I leave them unfrozen all the time for editing any at any time. Is it easier on the system to have all these streaming from 2 separate 500GB SSD's, or one 1 TB SSD? Thanks

Some of this depends on the setup and type of the other hardware in your system, generally speaking two drives will access data faster than one larger HDD. This is probably less noticed with solid state drives.
The SATA lanes to the motherboard have a certain amount of data throughput. It only stands to reason that two are better than one, since more data reaches the system faster. This is why I used two SDDs for my libraries. 
Everything is designed to multitask, so I maximize that potential.
I wouldn't split the same library across disks though, for instance I kept anything in Komplete on one drive. 

Thanks much for the info.