I haven't heard the ARC but have heard the NuForce which I would define as OPEN.
I had a Proceed HPA-3 and the Nuforce 9 easily beat it in my system. Will be moving up to the 9 SE. The Nuforce gear imho is very good for the price. Very natural and open. Would not be in the lush category. Extremely fast amps which will produce a tight accurate bass. Will easily control a big single bass driver which is amazing coming from a 7lb amp. Dbtrucks had these driving Wilson Sophia's and said the bass had never sounded so good coming from these speakers. Also, you can find a used pair of the 9.02's and if you like them Nuforce can upgrade them to the 9 SE version down the road. Right now I am using JM Labs Electra 936's which sound great with these amps. They give off a huge sweetspot together. Would love to hear your opinion if you get them since you have had the ARC.