I can't say I'd be disappointed with a speaker that comfortably extends down into the 30hz area of things. 30hz is very near the bottom of a piano's range - the lowest fundamental on a normal piano is an A0 at 27.5hz.As the 8361A costs the same as DD 8C and kii 3 but lacks the built in subs
Does it make it much more inferior?
Besides that, calling what the 8C and Kii have "subs" is a bit optimistic. Yeah, they reach down pretty much flat to 20hz - but look at Erin's distortion graphs. Both the 8C and the Kii are up above 10% THD down that low even at 86dB SPL. The 8361s on the other hand seem to genuinely not get severely distorted even in the bass region until you get up to eardrum shattering levels (up over 105dB/1m for one speaker, which is insanely loud). We're talking ~3% THD at 96dB/1m at 50hz in the 8361, if I'm looking at Amir's graphs right.
To reach that kind of distortion performance, the Kiis need subs - ideally, the BXTs, but that's close to doubling the price. The 8Cs need some kind of sub as well - I know my mastering engineer uses a pair of Rythmik F12Gs with his 8Cs.