I wouldn't say our 340's are overlooked, they remain extremely popular since we released them about 15 years ago. - They currently outsell our Sierra-1 and CBM-170's.
How one defines "better" when it comes to speakers is extremely difficult. One must understand and then define specific characteristics or performance. For music listening, the Sierra-1 will provide better imaging, a bit more detail, deeper and punchier bass and an overall smoother high end. The 340's will provide better mid-bass, provide higher SPL's, and will have a slightly more clinical presentation.
Some of our customers prefer CMT-340 over Sierra-1 for home theater, while they prefer Sierra-1 for music listening.
It really comes down to what you are looking for in your speakers -- which is often difficult to define until you really get into critical listening. And when one starts critical listening and builds these skills, differences between speakers become much more apparent.
For example, I would say for someone new to this hobby, they might even prefer the CMT-340 over our Sierra-2. But as time goes by, and critical listening skills improve - one then generally prefers the speakers with a more accurate and more detailed presentation, thus craving speakers like our Sierra-2. Customers often ask, for example, is the Sierra-1 10-20% "better" than the CMT-340? The proper response to this is always, "it depends on your critical listening skills"... For an experienced listener, that difference in performance can easily be huge, for the non-critical listener - they might not even hear a difference....