2000tlnavi

i'm not really interested in having video in my car. therefore, i'm most likely going with some variation of audio only double din receiver. it will be cd/mp3 compatible. i'm considering the Kenwood DPX-501 (which is not out yet). are there any other decent audio only double din's out there? initially, i'm going to only be able to replace the HU. how would the OEM bose speakers sounds with a new deck? should sound better right?

when i have the funds i'm going to upgrade the speakers. what size speakers will i need? i can use 6.5s all around, right? what kind should i get? i've heard good things about diamond audio. i'm looking at the diamond audio d6 6.5 components in the front and their basic d3 6.5 coax in the rear. anyone used diamonds before? will i have to amp them? or can i get by with just the power from the HU?

TIA