I installed Light Harmonic upgrade over my standard audio on Saturday. It is clear improvement to the cheap lightweight speakers, but you can only go so far by replacing the elements. The door card and attachments are clearly not too well designed and resonate even on moderate sound levels so much that it causes easily audible distortion (a second culprit was found, though). As comparison, my year '00 Audi A8 door cards do not resonate on touch at all (and I mean nada) before reaching distortion levels from the Bose head unit. That is a design released in '94... Bass is nice and firm without subwoofer for my needs, which is rock music. I saw this video today and got inspired (starting 1:40) 1st finding: speaker grille pops out easily. 2nd finding: they had added some cellular plastic around speaker bodies, and I thought that might be worth trying. Oh yes it was! I had some Armaflex (19mm) cell rubber insulation lying around, and I cut 2 inch wide strips, which I tucked in the gap between front speakers and door. I used same interior vinyl tools for tucking as with the door card removal. Be careful when doing this, as it would be very easy to make a dent in the speaker cone, as you'll need to apply force. I left upper part without armaflex, as it seemed risky to tuck it blindly behind the door card. If I'd remove the door card, it would be easy to do around the whole speaker (I'd use glue).. I also applied Stp Black Gold (aluminium laminated butyl) on all surfaces, including inside of grille smooth parts and inside of door card, for the small area accessible through the grille. I had already put this on the metal parts of door (but not on the door card) while doing the LH upgrade. One of the major culprits of the boomy, resonating bass was found: there is a bass port hole behind the grille! I tucked these full of armaflex. In fact there was already a small piece of some kind of softening material in rear port holes. If you do nothing else, try at least this! It can be done and undone in 5 minutes. You can see the hole open in the video, and tucked in my photo. For rear speakers, there is no gap visible through the grille, so covering around them would be needed to be done when the card is removed. Since I just did the LH upgrade on 2 days ago, didn't have the motivation right now (plus it is night time over here). Port hole armaflex and Stp treatment did some good though. All this really made a difference to the firmness of the bass and lower mid range. Resonation is less and bass distortion from the porthole is less evident. The sound is no longer tiresome, especially after toning down upper bass with EQ (a DSP would really do the trick here). Now I'd say it has been upgraded from standard audio poor level, and LH acceptable level to ok/good level. I can now listen on level 6 or 7 without annoyance, before it was 3 or 4). For how easy this was, and for estimated cost of 5 euros for material, the improvement is even better value than LH upgrade, which cost about 1k€, no doubt. Same trick could be tried for the UHFS or standard audio as well with what I expect would be an improvement in each case. I think they should supply this stuff and instruction with the LH kit!