I also have the Seagull S-6 and 14 other guitars and I think 4 only cost me $ 140.00
I remove the cheap strings and install ELIXIR MEDIUM.
I also cange the bridge and nut to the bone type on the cheap guitars.
Check out this site because if he dosent have what you want then they don't make it.
The strings are priced lower then any oter place I checked and they not only sound better but last 5 times longer.
BOB LECH
http://www.guitarfetish.com/Phosphor-Bronze-Acoustic-Guitar-Strings_c_369.html