My A/V receiver does not display absolute db of volume level, but I need to turn the relative volume from 24 to 21 to maintain an audible balance when switching sources. This is when the A/V receiver is fed with digital audio from the TV.
I would rate my system volume change between Tablo and live TV (the most fair source comparison) to be more in the "just noticeable" range but not a blasting difference.
Since the Tablo audio first comes thru the HDMI cable from the media player, I suspect the various makes of media players could output different volume levels, which could make absolute comparisons difficult.
Comparing the output volume of the Tablo played thru a media player to the audio level of an Internet streaming source on the same player may be an unfair comparison. The audio level of the Tablo should more closely match its recording source, which is live TV.
I would have no problem with a 3db increase in the audio power level of the Tablo. I would not be in favor of a true audio level double which should be in the 6-10 db power increase, based upon some Internet references.