96 mazda 626, head unit

Hi!Just bought a 96 Mazda 626. I want to change the head unit to a stereo with an aux in. The car already has (I think) an aftermarket unit. It's a Blaupunkt Munchen 106. I guess it's aftermarket because of the way the wiring is behind the unit, the fact that it's a Blaupunkt and not a Mazda own brand, and that it's a CD playing head unit (unusual for 96 on that spec car?) etc.If I could get some help with this post I would be really grateful.The way I understand it is this:-Cars ship with non-standard stereo wiring and if you want to replace the original head unit with an aftermarket one you have to splice the wiring into an ISO connector.-This has already been done on my car.-This means that I can buy a new stereo and just pop it into the DIN, connect up the connectors (are they ISO - can you tell from the pic?) there are two connector blocks, a thin yellow wire I have no clue about and an antenna-The only thing I'll have to fiddle with will be the antenna - the hard work was already done when the first aftermarket was installed.Can someone check my pic and my hypotheses and just tell me if I'm on the right track or not?! Thanks!

i.e., do I need one of these or do I already have one fitted? In the picture above, there is another connector underneath the brown one.