Do not use a SATA adapter, SATA drives will not work properly on the empeg even through an adapter. It must be an IDE PATA drive.

If you want to go with a solid state drive, your best bet is a CF adapter. CF cards are just like IDE PATA drives in terms of the pinouts and the way the firmware addresses them, so they will work best with the empeg. (Also don't go with SD either, it has other problems.)

I was happy with the following:

Adapter:
https://www.amazon.com/gp/product/B0036DDXUM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Card:
https://www.amazon.com/gp/product/B00NUB2TWI/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

A couple notes about that CF adapter:
- It doesn't have a master/slave jumper. Instead, you plug the CF card into the adapter's Slave Slot or the adapter's Master Slot to switch it back and forth.
- I don't trust the CF card's ability to stay in the slot with the empeg riding in a bumpy car. It's only held in by the friction of the pins themselves, there's no clamp mechanism. So I put a piece of strong tape across the top to keep it parked in the slot.

Regarding size: CF cards only get up to the range of about 128-512 or so, it's hard to find anything bigger. Your best bet is a single CF card of about 128gb or 256gb. Make sure it's not a "CFast" card because those aren't the same as CF/IDE/PATA either and will have the same problems that SATA or SD would.

Make sure to use Mark Lord's latest files for setting up the new drive.

Also do not attempt to upgrade the RAM of the empeg player, it is risky (it can brick your player) and it won't help any of the issues. At most, upgrade the drive to a solid state CF and call it good.

Most likely the rotary encoder is the thing that will give you the most trouble out of everything.