Like Nonoise, I own a Marantz PM15S2 also and cannot say enough good things about it. In fact, it replaced Parasound seperates and has taken my 4 Ohm Vienna Acoustics speakers to new heights.
To also quote you Bokkus..."build quality is my main concern". I think you would be hard pressed to find an integrated amp on your list, or any other for that matter, as well built as the Marantz PM15S2. Well maybe its big brother, the PM11S3. Both are built at the Marantz reference factory in Japan and they just exude quality. Seriously, check one out and audition it if you can. Ask the dealer to use it with his best, most expensive speakers too. The Marantz will be up to the challenge.