Video Editing DAS with Synology NAS

As a filmmaker for many years, I recently upgraded my portfolio to a Synology NAS 1621+ Which I filled with Seagate Exos X20 drives which are RAID 5 and have a 10gb hardline connection to my PC.

My workflow speed have been tolerable with only a few times where I feel like I’m bottlenecking somewhere. Obviously if i had the money I would have gone with SSDs but if i am wanting a faster read speed when editing should i be looking at getting M.2 cache drives or more ram or both for my NAS?

My PC has a Ryzen 9 5900X with 2 x 16GB of DDR4 (Maybe i should upgrade the ram)?

Not super nerdy when it comes to computer stuff just a camera nerd so go easy on the lingo …

Cheers