A little belated finding this thread but...
It is difficult for me to prefer one over the other largely because either were manufactured possessing beautiful/handsome esthetics apart from their very decent - even by today's standards - sonic qualities. The Marantz receivers probably inch a smidgen ahead because of the horizontal tuner dial and the cool blue lighting, but the Pioneer receivers to my ears just sound better overall. IMHO, of course.
I have two Pioneer SX models, a 650 which is still being used in my girlfriend's bedroom system, and a 1050 which I reserve as a backup in my home system. In my girlfriend's living room we listen on a Marantz 2250b hooked up to a pair of Meadowlark Kestrels, which I think are some of the better speakers I've ever had, especially at the price I got them at -$400 used. Barely.
While my current system is superior to either receiver, I continue to be pleased with their sound, their looks, their quality. If I could relate to them as cars the Pioneers are vintage Chevies, the Marantz are Saabs. I love Saabs.
I've hooked up the SX1050 to my Thiel CS3.5's and found little lacking. Were I to find myself having to let go of my current gear I wouldn't be too saddened by having the receiver act as my sole source of music. It's still that good. At 40+ years of age that's saying a lot.
