Interesting... I have certainly heard this criticism of Cyrus before.
From what I can hear, it could be the "leaness" in the sound that causes it to become wearing over extended listening. Perhaps this is what some people perceive as forward? To my ears the Cyrus isn't forward at all. In fact, I'd say sounds more even handed than most.
Having said that, it defnitely isn't for everyone. The perceived lack of body to the sound means that those seeking euphonic warmth need not apply. This isn't very high on my list of priorities however which is why I'm rather enjoying this little amp's sound.
However, as I said, the little Cyrus isn't without flaws. It's just that it's weeknesses are such that the musuc remains intact.
Lefty