I'd still check out Red Wine Audio. A Pass or Boulder integrated will give you a whole different experience, but will be more pricey, but they're also rather more linear than what it seems you've tried. Assuming your Merlins are like my Merlins then they can easily handle a more neutral amp. They'll also respond well to a amp that has a great grip. Since last year, I've upgraded my amp to a Plinius SA-Reference (just because) and I have *never* heard Merlins with this much bass power. It's crazy. My two subwoofers are now sitting completely idle, off in a corner and gathering dust.
Here's another thought. What cables are you using? If you're using the Merlin recommended Cardas, I humbly submit that perhaps you're not doing yourself any favors, esp. if you're not satisfied with the bass response of the speakers/amp combo.
