I had the same decision in front of me and went with the 4500H as I got it for less then the 3700H in sealed box with full warranty. The 4000 Series just offers a lot of upgrades hardware wise including more powerful amps with lower distortion, a more powerful power supply, gold plated contacts throughout, a 2 line display, more inputs & outputs, more 12V triggers, more metal & less plastic overall(it weighs almost 4 pounds more). It is a far better value at the same price point features aside. Now, ultimately an amp also has to have the features you need so, that must be taken into account too. The one thing the 4500H is missing I wish it had is Atmos Height Virtualization but, I can live without it.
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