Need help with storage/expansion options

I have a retina 5K iMac with 500 GB SSD. I have OS X, my music, and my files on the internal drive.

I also have an external LaCie Big 1 TB drive that I use to store my photo library. I have a couple of HDDs in external enclosures that I use for backup 2-3x/wk.

Overall this setup has worked well. It is almost completely silent, which I require because I do a lot of audio recording. And it is fast, which I like because I'm really into photography and I have a full-frame DSLR that produces large files, which I process in Lightroom and Photoshop.

However, both my internal drive and LaCie Big are starting to get quite full. If I could go back in time, I would have bought the 1 TB internal SSD with the iMac, but I didn't—and as far as I can tell, there's no way to upgrade that, right?

I would really like to increase the storage size for my photo library, as well. But I need to have a completely silent external drive. I can't have an enclosure that has a fan. Right now the only option I can see is getting another LaCie Big and daisy-chaining it to the first one, and creating a RAID-0. This would give me 2 TB of *very* fast storage that is completely silent, but it only adds 1 TB of space for $1,300. This would allow me to move my music and maybe files off of my internal drive, to free up space there, and still have 600 GB or so extra space for more photos.

Are there any other options here, given my needs? Thanks.