Integrated brand choice -- Simaudio, Hegel or Mark Levinson?

Agree with a few other on here regarding the Luxman. I bought my first Luxman integrated amp earlier this year and its by far the best amp I've ever owned. You should definitely consider a 507UXii.

Agree with the others about the Luxman 
check them out. 

I would agree with bluorion, the 507UXii sounded beautiful when I auditioned it recently.  Smooth, powerful, and intoxicating.  It was a very hard decision when I went with the Hegel 390 instead, but I knew I would be super happy with either.

I have a Simaudio 680D Stream Dac hooked up to a Anthem-Str Integrated amp with Focal Aria 936 speakers. I know the the Simaudio cost way more than the other parts of the system but I listen to streamed music mainly. I plan on up dating the speakers at some point and maybe amp but it really sounds amazing. The source is very important too.

With Focals I'd err towards Luxman, Accuphase, Pass, Ayre.

The Belles Aria Signature integrated is available nowl; the Virtuoso integrated will still be a little while coming.