Hey Zachary, you'll want a pair of good ΒΌ" TRS cables to go between the FocusRite and the speakers, both the Scarlett and the Eris 4.5's have balanced jacks (which is nice). Of course you can spend a TON for Mogami or Monster cables (which I have), but these LyxPro and now finding their way into my studio and live acoustic rig, and they are very well made:
https://www.amazon.com/LyxPro-Balanced-Crystal-Noiseless-Flexible/dp/B07198F4CT/ref=sr_1_14?ie=UTF8&qid=1516819692&sr=8-14&keywords=trs%2Bcables&th=1
The TRS cables plug into ONE of the Eris 4.5's, then you simply need good ol' speaker wire to run to the other cabinet. Here's my suggestion:
https://www.amazon.com/gp/product/B00NSGCVWI/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Great wire, it's really flexible so it immediately lays flat when you unravel it. And it's a really cool two-tone blue to match the blue theme of the Eris design.
Enjoy!