Firstly, if you want a no frills, simple and reliable amp, then go for Norge. Norge amps are neutral to slightly bright in comparison with Marantz, but that brightness is also required if you want to be involved in the music you listen to, but if you prefer to listen to music in the background, without much involvement, then go for Marantz as it is a neutral to laid back type of amp. Marantz has slightly more bass in comparison to Norge. Other aspects of audio quality are more or less the same in Norge and Marantz. Yamaha can be clinical.
Secondly, take into account the service and maintenance aspect. New versions of Marantz may not be locally repairable and has to be sent to service center, whereas Norge is locally repairable. You have to decide which is more feasible to you.
Thirdly, Norge with it's own speakers is the best, but of-course you can use your Sony speakers for now and later opt for Norge speakers.
Sony is inherently bright, but that can be controlled from the amp's tone controls. If you opt for Norge 1000 Gold, then always pair it with 8 ohms speakers, never with 4 ohms. Norge 2060 can be paired with 4, 6 or 8 ohms without issues.