I don't know if the SDS100E are any different in its electrical design, but I use a big 2 ohm speaker and volume at 5 to get a comfortable loud sound at my desk.
Its a little on the high side but I have the Valor lapel mic and it works great. I use my SDS 100 while on fire scenes taking pics and with all the noise it is perfectly clear.
I've actually ordered a portable bluetooth speaker that can be hard wired to my USDS100.
I'll see how well that works first before trying other ideas.
I can also use it for other things.
Plug in any speaker you have, USDS should also be able to handle any low impedance speakers, and it will be a big improvement over the internal one. The speaker amplifier in the scanner are protected for both temp and current and power so can never be destroyed.