Yeah, that exactly what I've seen, anything drive over 7TB is just not recognized. (The T7 you found is just a 2TB drive. I have a couple of those very compact babies for my Acronis or Carbon Copy Cloner full PT/MAC backups. )
Maybe because they left a little room for you to plug in a smaller 1TB 2nd drive? The funny thing is that hardly any manufacturers have EVER made 7TB drives. They go from 6TB to 8. The way I got my 7 is that I bought a 5600 rpm surveillance drive which does/did come in 7TB sizes..
As for SSD's, that's been discuss at length before. Just do search on SSD. It's not about the R/W speeds or amount of R/W's, it's about the fact that cells in a SSD can only be used a certain amount of time before the are marked bad or burned out. In which case the internal SSD controller has to fool the operating system and move the block to another part of the SSD and lie as to where it actually is. With enough R/W's which the Hopper does whether it's on or off and SSD can fail very quickly.
Now, if you just want to use it as long term program/movie storage and leave the programs alone, and SSD should work fine. Other than you'll see or gain no performance improvement as the Hopper will pre-buffer anything played back from the EHD, just look at the lights, the EHD will blink about 5-10 seconds before the next scene is displayed. The hopper if pre-reading the next set of blocks to keep the stream continuous. Add the fact that the max transfer speed is USB 2 (not 3) and you are limited to USB 2 speeds which just about any Hard Drive will easily loaf though. That's why the Hopper pre-buffers the program because it can't pull the data fast enough off the EHD to keep a constant video/audio stream so it has to read ahead.