Peter , I wonder wether you should take this up with the Morgan top brass as the quality control here leaves a lot to be desired in such a desirable Mog as yours is. They should be ashamed of themselves .
There have been many posts here about quality control and attention to detail at the "Factory". They know that they need to do better and have made progress: the general level of fit and finish on our 2014 Plus 8 is way ahead of the 2009 Roadster.
BUT it seems that car audio is something that no one at the factory really understands. They can't get DAB radios to work, yet the answer cost me £30.00. I suspect that they don't believe car audio is very high up owners priority lists. For Traditional Morgans I think they are right but for the Aero based cars, especially the new Aero 8 with its beautiful hard top they need to up their game. It is pointless providing a tablet based system if the rest of the audio installation isn't good enough.
I agree Peter, I replaced the terrible speakers in the footwells on my Roadster with JBL's which also have a separate tweeters. I paid £38 for these as end of line sale for 50%.
The difference is quite pronounced even in a trad. I too have replaced the Alpine head unit with a JVC dab multi media unit that I already had and simply put in the DAB radio splitter, as you did, and it works great. The Alpine unit is quite good actually and is in the Cooper S now.
The speakers that were originally in the car I reckon cost no more than £15 a pair and any reasonable volume resulted in distortion and just weren't worth listening to. I can now cruise and listen reasonably well up to 60-70mph, its not perfect as its not a tin top, but is usable. Come on MMC put some decent speakers in the cars, not cheap rubbish.