I'm looking for some advice on upgrading my existing setup.

I currently have an old Sony XR-C510 h/u, external amp driving front
component speakers and an amp driving a small 8" sub (using bridged mono)
and a Sony CD Changer. I'm generally pleased with the quality but I'd like
to spend some money and upgrade with the possibility of playing MP3s.

I've narrowed my choice in my price range down to the Sony CDX-M850MP and
the Pioneer DEH-P77MP. Since I have an existing CD Changer my thought was
to go for Sony in order to use this kit and then upgrade in the future to a
MP3-capable one. That way I can start to use MP3s with the slot in the
headunit and still make use of the changer.

However, there are 2 downsides to the Sony I feel. One is that it looks a
bit tacky (IMO) and the other is that it doesn't have a detachable front
panel. At the moment I'm not too fussed about the security of my headunit
since it is so old and not really worth nicking, but upgrading changes that.

This is where I hit on the Pioneer - looks are beautiful IMO (esp in my car
which is a Merc - I don't think the Sony would blend in well with the dash
and general feel) and the detachable front. Of course the big down-side is
that I will have to ditch the CD changer earlier than I thought.

What I wanted to get was some advice on the sound quality/features of these
two units in comparison to help me make my choice. At the moment they're in
balance for my situation, although reading around it looks like the Pioneer
may have the edge with its higher output pre-outs and good control of LPF
and HPF for tweaking my sub balance. I did also notice the Pioneer has Burr
Brown D/A convertors which is a name I remember of old in the hifi world -
but would they make much difference? And it also plays WMA files which I
don't know much about - reportedly they are smaller files for the same
quality.

Price is not an issue since there's only 30 GBP difference at incarexpress.
Obviously the amplification stage doesn't interest me. Overall I guess I'm
looking at the longer term use - should I stick with Sony or do I take the
opportunity to change the system make now for the future?

I listen to a mixture of Classical, Jazz, 80s/90s pop/rock.

Any thoughts?

Thanks,
Pete.