Must have been an old merc, as upgraded audio on merc for last 5 yrs has been beaumiester (spelt wrong i know)I hope standard audio is not tragic, if it's average, it's fine. I would rather have spare wheel, than subwoofer in the boot. Spare wheel as standard on UK VZ2 spec was nice surprise, as most manufactures phase it out and you have to pay extra to get it back.
I went through 3 cars with Bose, 2 or 3 with Harman Kardon and one with Dynaudio. I'm not sure if HK was better than standard Merc audio. In one car I bought, it was switched off in menu, so there's a chance first owner didn't even use it.