If you use tinycore-redpill. Boot as IDE, then after you finish building the bootloader via
./rploader.sh build ...
then, you can switch back to SATA.
Then for SATA to work, here's how I got it working:
Use SATA DOM boot arg
For this to work, you must choose a model that supports SATA DOM, such as DS3615xs.
All you have to do is add the following boot arg:
synoboot_satadom=1
You don't even need VID or PID.