Take the trade and the money. I think the 27da will be easy to sell in this market and with summer coming, it should sell and you will soon be a one boat owner.....
Did you haul the boat and make sure that nothing is growing inside the thruhull fitting? I have found debris in the pick up that redirects the water flow the faster you go. Why do you have to wait so long after you stop to restart? If you still have no water flow once you stop, the unit is...
The Master A/C unit is the furthest from the pump. I would suggest flushing the complete a/c system. You will notice better water flow to all the units.
MB Quartz makes some nice speakers that I have installed as upgrades in a couple of S/R yachts. As far as an amp, I like the clarion 480m (best for plug and play) Better upgrade is to go a Diamond audio amp, will need to run large positive and negative cables to power, but worth the money and...
vitracore is no longer avail, even if you can locate some, it is crazy money. The idea of removing the frig panel is cool. Just be careful remove the panels, vitracore like to crack very easy.. You can also look for mica that may be a close replacement to fit back into the refrig. Good luck