When I had the ES-1, I did not have the FS, so it is hard to compare them from memory - but it is the same tech employed, so I do believe there is a family resemblance to the sound.
I find the little FS to be a great little unit. It is ridiculous to see it with my huge open baffle speakers, but close your eyes, and it does the trick.
I am hoping that the EX A1 will offer some improvement - in reading about the attention to detail employed in voice it (separate power supply, caps chosen for sound, copper screws etc) it should bear out that way.
If it does, I will likely use it AS my system... with the Visatons, and some subs. The wooden speakers I will use in another room, likely with the FS.