jd_watt, I think you experienced the Fletcher-Munson effect. It will make things sound bassier and also with a bit more top end as the SPL increases from low (bedroom) to high (gig).
This phenomenon is what "saves" most of the "regular" bass cabs, as they are very rolled off in the lows. The SVT-410HLF (like the fEarful 15/6 etc) is also rolled off, but not as much. These latter cabs, including the HLF, are actually giving a truer representation of the lower register in our instruments. They will also be more revealing to gear or player shortcomings for the lows. The SVT-410HE and most other sealed cabs will roll off and (at high levels also severly compress!) the bottom octave, thus removing the potential issues related to "true lows on stage". (Interfering with the PA, bleeding into kick and other mikes, exciting room resonances etc.)
As always, defining needs and goals before purchase can be hard, but without those facts it is easy to get REALLY disappointed with any product.
I am very pleased with my Asian HLFs, but I know the US made ones are too dark for my taste.