I revoke my recommendation for the Def Tech. After more googling, I'm inclined to agree with zieg, that the frequency response rating on Amazon was too generous. I assumed that it was like most other Def Tech gear and had passive radiators improving the bass response, but I guess not.
Anyway, the problem with speaker reviews from consumers is that speaker response is very heavily influenced by the room in which they're played. That's why auto EQ and distance calibration of receivers is usually referred to as room correction, rather than EQ. Receivers still reduce some frequencies to tame peaks and attempt to flatten the response, but the term "EQ" has connotations of user preference that don't have much place in correcting room response. But I say all that to say, most of the unfavorable reviews you might read were written by people who have made no attempts to tame their room response. They may have nodes or nulls in places that make speakers sound thin, nasal, tinny, and every other adjective you see. But their room is not your room. What sounds like garbage in someone else's house might sound like angels singing in yours, or vice versa.
That's not to say that any piece of garbage will sound as good as something decadent in your room, though. A speaker bar with poorly designed crossovers might sound muddy no matter where it's played. One with a plastic cabinet will sound hollow. One with cheap plastic tweeters won't sound as airy or revealing as one with titanium or similar. So you can gauge a little if you can get an idea of the construction without falling too much for the marketing speak -- for example, a "1-inch silk polymer dome tweeter" sounds impressive until you realize that polymers are just another name for plastics. On the other hand, don't discount paper-cone woofers just because they're paper.
Shopping for speakers without listening to them is hard. And even if you can listen to them in the store, they will probably sound different in your house.
I like to shop based on a company's reputation for solid, well-braced, inert cabinets; well-designed crossovers with dependable grade components; and try to find professional measurements. The measurements part is very difficult for sound bars, though. Wouldn't it be nice if speaker manufacturers would publish a response graph with their products instead of just a range?
Anyway, Polk is not a company that I would say has such a reputation. Any thoughts on the Klipsch?
If you do go for the Boston, then you'll have more money to devote to a better sub, which is easily the most influential component of your home theater. That's not a bad thing.