Hi Ankit,
I just saw your thread,
Like others have told you, Bluetooth is absolutely the worst way to send audio to the meridian.
Also I would leave recommendations like damping alone unless you are facing vibrations. RR are fairly sturdy vehicles. Plus, you really need a good installer to ensure no damage is done opening the door pads.
finally, don't think too much about quality of DAP for the Audio in. In all probability, the audio-in / aux-in is digitised for dsp processing, so all you will hear is the quality of the ADC and DAC. I would focus on sending the sound digitally to the car.
Most HUs are optimised for iDevices. if you have car play, then tidal, etc will play without issue. even without, the iPhone lets you control all modern music apps from the iPhone player in the car. (see the photo below on Roon running through an iPhone on a non-carplay interface. tidal runs similarly) If you don't use an iPhone, instead of buying a DAP, buy a used iPhone instead. run it without sim may be to just work as a DAP. and it can use the hotspot of your current phone.
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EDIT: if you do this, you will be assured of the best clarity the system can approach. If that is satisfactory the next step is tailoring the sound signature to suit your ears. For that there are many approaches and a lot depends on what music you listen to - Streamed music like itunes, FLac files or .AAC or mp3 files.