Need some guidance on speaker replacement....those in my '96 LX450 have seen better days!

Can someone answer these questions, or at least get closer than I've been able to:
(1) What exactly is this so-called premium sound' in my '96?
(2) What replacement speakers can I use in the front and rear doors which will allow me to still use factory grills without the use of aftermarket spacers?
(3) Any center console 'sub' replacement available?

Thanks in advance. I've been trying to get straight answers to these for a while....I should have stopped here first.