Marantz is known for exceptional music performance. If you think otherwise then you obviously dont know Marantz. But yes they also do a fantastic job with HT.
I just finished a thread of a review on the Marantz SR6003 (which is extremely similar to the 5003.
http://forums.audioholics.com/forums/showthread.php?t=52159
In the past few months i have used an onkyo 805, Denon 2809ci and 3808ci, Yamaha RX-V3900 and RX-V663, Emotiva LMC-1, Emotiva DMC-1, and most recently the Marantz 6003.
The Best performers by far have been the Emotiva DMC-1, Yamaha 3900 and Marantz 6003 IMO. The Marantz has pretty much zero bugs and the yammie only had a few for certain people using certain cable boxes. For the money and performance that it offers i really recommend the Marantz. The SR5003 is a steal at the $549 price.
But of course everyone has different opinions and different equipment, so these are just my little thoughts
-Steve