Should I return this SVS SB12-NSD?

Have you given the guys at SVS a call. They'd love to help you with your dilemma as my understanding of their customer service, they want you to be happy.

I have the same sub, got less than two weeks ago, and it is extremely impressive in a 30x17x10 space. I would be extremely surprised if you are finding that the Energy sub outperforms the SB12-NSD.

Have you tried different placement options to see if that improves the sound quality? Have you done the sub crawl? I am not doubting your experience, but there might be more to the SB12's performance (or lack of it) in your setup. What did SVS walk you through, that you had already done? What are your crossovers, sub's amp hookup and settings on the back, etc.? Did your Yamaha receiver have YPAO room correction capability, and did you run a calibration using it?

First of all, your Energy sub's mid bass was most likely a good part harmonic distortion. Higher order harmonic distortion will always sound like exaggerated upper bass. It might have sounded punchier because it was playing stuff that doesn't even exist in the original recording. The SVS subs are very good at keeping harmonic distortion down, and as a result the sub might not seem as punchy as you are used to. It's hard to believe it isn't getting louder than a 8" 60 watt RMS sub though.

I would also add for adding strong bass to electronic music, the SB12 is just about the last sub I would buy for the money. It's mid bass output is just not very good, as can be seen here. I don't know why you think this is the market's most musically inclined sub, considering that dynamic range is a part of music playback, and that is not at all a strong point for the NSD subs. I suppose for the people who determine what makes a sub musical, smooth jazz is the only legitimate type of music.

Some similarly priced alternatives you might consider are the Premier Acoustic PA-150, Hsu VTF3 mk4, and the Power Sound Audio XS15. The PA-150 costs a lot less but will still have multiple times the output of the SB12 from the mid bass region and above. It doesn't have much deep bass output, although it still has more than the SB12. The VTF3, on the other hand, has a ton of deep bass output and lots of mid and upper bass too, but not quite as much as the PA-150 or XS15, although it will still have a lot more than the SB12.

I have had my SB12 for a few month and for me it is great. My room is a bit smaller than yours (12 x 12). I have the slightly larger energy take 5 classics. I found 120 crossover worked best for me. The SB12 kicks butt over the old energy sub (which the amp failed after 2 years use)

it did need time to break in before it really sounded good.

But at the end of the day if it don't sound good in your room ... send it back. Look at the PB1000 if you don't have to have a small profile sub.

A single SB12-NSD in a 3700 ft^3 room is a bit of a mismatch unless your playback level is moderate. If you are pushing the system loud and looking for more slam/impact/pressure on action/sci-fi Blu-ray DVDs, the larger PB12-NSD (which has 2-4X more max output in the 18-36 Hz octave) is a better choice for that size room. Also upgrading your speakers to models with larger/multiple mid-bass drivers will add mid/upper bass dynamic output capability, and also allow you to use a deeper speaker/sub crossover (160 Hz is pretty high and makes the sub pretty easy to localize).

Extrapolating on my previous statement, the SB12-NSD, PB12-NSD and PC12-NSD all share the same 400W amp and 12" NSD driver. But the larger PB12-NSD and PC12-NSD subwoofers are 2-4X more powerful in the all-important 18-36 Hz octave - which speaks to the benefit of the larger enclosure volume and bass reflex alignment. At higher playback levels on bass-intensive Blu-ray DVDs, the subjective differences between the SB12-NSD and the larger vented NSD models are very obvious. If available floor space is a consideration, but you don't have height restrictions - consider the PC12-NSD which delivers the same performance as the PB12-NSD but with only a 16" diameter footprint.