I think the difference is to be found in the stressing of the syllables: domaren has the stress on "do", with o slightly long and pronounced more as [u] (in IPA), "ma" [a] and "ren" [e] or [ə], both short. De är en has a short [o] (and not [u]!) in "De", and I think "är" would be stressed with a longer ä which is not properly pronounced as [a] but rather [ε] or [æ], and afterwards en [e]. So /'dú.maren/ or /'dú.marən/ - /dom'æ.ren/. Please feel free to correct me since I'm neither native anglophone nor Swedish.