I don't believe TME ever offered an exhaust system for the Amazon so if it is a genuine TME product its a retrofit from some other car. Definitely not a 'commonly used product' on an Amazon. TME / IPD offered a SS sport exhaust system for the 740 turbo with only a back muffler with the tail pipe tip mounted directly to the muffler; but, it was an oval, not round muffler.
IPD did (does?) offer a sport exhaust system for the twin down pipe Amazon made by Simons. A whole bunch of other vendors sell the same system. I believe it does have a round rear muffler; but, the tailpipe is attached directly to the back of the rear muffler. It also has the really long, straight, muffler / pipe thing up front.
If your TME muffler is a straight through absorption type muffler and the internal pipe is 3" in diameter and its the only muffler in the system, I predict that the system is going to be really loud. Your muffler shop go is probably fairly accurate in his assessment. Also, a 4" diameter exhaust tip on an Amazon looks silly unless you are attempting to channel a ricer boy look.
I have an IPD cast aluminum valve cover on my B20E. Any reduction in valve noise was in the imagination of the copy writer who prepared the IPD catalogue. The primary benefit of the cast aluminum cover, aside from dress up value and providing rocker clearance if you have a high lift cam is that it is rigid and resists deformation around the mounting holes which greatly improves gasket sealing reducing the inevitable oil leaks. My valve cover was black with polished ribs on top. If your valve cover is the same, the best thing you can do is clean it and take it to a powder coating shop and have it powder coated with a high gloss finish in whatever color you want (except black). Mine is silver. The black finish on the IPD cover accumulates dust and oil like crazy and looks like crap in a week or two. If you want to maintain the dress up factor, get it coated in a glossy finish that doesn't trap dirt and is easy to wipe off.