Efficency- Low vs. Hi?

I agree about the mismatch. My view (with all its biases):

PSB Stratus Mini: described as having great bass (for size)

Cambridge Audio: UK company with the "British sound" (warm)

Not having heard either of these, I'd expect an overly warm tonal characteristic that essentially hides the midrange that may be what you've described as "shut-in."

My guess is that efficiency is not really the issue though one can make some generalizations (a dangerous idea at best). That is, that lower efficiency designs tend to be more controlled hopefully with a more neutral tonal balance while higher efficiency designs let through more of the speakers inherent characteristics which includes colorations (the peaks and such mentioned before). IMHO, higher efficiency designs have a more immediate quality / quick response that provides a sense of openess (certainly not "shut in").

My inclination is to get the warmth from tubes rather than solid state components designed to sound warm and match them with high efficiency speakers that give immediacy and openess. It's just one approach. There are many others. Thinking through what direction you'd like to go with help from others at stereo shops might be useful.

Your taste is pretty bass-heavy. Grinding, crunching, woofer-throwing music isn't generally regarded as the stuff hi-eff is made for. Inexpensive, hi-eff, big bass? Hmmm. . .gonna have to think about that one.

For that musical taste, I'm thinking a used 150-watt+ amp. I don't think your amp is gonna push the power you need with any speaker. Just one opinion.

Danner,

The midrange is actually MUCH too forward, anything with distorted guitar and/or yelling vocals is utterly unlistenable. Much too grainy ,harsh fatiguing whatever you wanna call it. This type of music takes up about 90% of my music collection. Its not the room either because i tried my system in two different rooms, one being large and one being small, and in both rooms the sound was almost identicle. However, what i meant by "shut it" was that the soundstage, imaging and detail sound restrained, almost "lazy". The bass is also very lean and weak sounding, even in a small bedroom. Im really confused on what the problem might be. Thanks for your response.

Dave123etc. - I'm not reccomending tubes per se. I've got similar musical tastes to yours and also low efficiency speakers. Tubes were part of the answer for me, but a lot of folks would like solid state just as well or better and would be able to find a more cost effective solution going that route.
Back to your original question, I went with a low efficiency speaker only because that was the one that happened to knock my socks off. Ida preffered it if I fell for a higher efficiency speaker, just didn't work out that way.
Good Luck!