A lot of that depends on the music you listen to. 38Hz is "enough" for some things, but a sub wouldn't hurt in the slightest. Of course if you were to connect those GS10s to a more capable amp than your receiver you will probably notice quite a bit more bass... When I went from receiver power to a 200WPC Rotel AMP on my N804s, bass suddenly came to life. The real problem was my receiver couldn't power the low end with any authority.
I would set things up, then see if you need to add a sub later.
Mastering and 2 Channel: Wavelab 9/Bluesound Node/Pro-ject RPM 5.1 SE -> McIntosh C47 -> McIntosh MC452 -> Focal Sopra No 2 and REL S5/SHO (switchable)
Mixing and desktop: Cubase/Squeezebox -> Oppo HA-1 -> Rotel RB-1080 -> B&W N805 and REL S2
Theater: Oppo 103d -> Marantz SR7009 -> Martin Logan Motion 4/8 7.1 with REL S5/SHO
Living Room: Marantz SR5009 -> Rotel RB-993 -> B&W N804/HTM1 Rythmik F12SE