The fundamental is somewhat difficult to hear, though you can. When they say human hearing only goes to to 20 hz, that in reference to to discerning speech and whatnot. That said, C#0 (and below) is felt more than herd.
Also even though you can hear many of the overtones much better than the fundamental your brain will reconstruct the fundamental based on the harmonics.
I remember Yves Carbon using a low low B (around 16Hz) and it was perfectly audible due to his perfect Nogera bass and the marvelous overtones it produces even on records. I know Jauqo III-X use a low C# tuned fretless 4 strings with great success.
I've ordered a 9 string from AC Guitars in Moffat, UK A.C. Guitars - Hand Crafted Basses & Guitars which will be tuned F# B E A D G C F Bb. There's a thread on this part of the sevenstring.org forum.
The thing about ERB's is that they may look pretty scary, but they're usually quite easy to get around on. I bought a Conklin Groove Tools 7 string a few years ago and I have a 7 string from Sei Bass in London, UK Welcome to the Sei Bass Homepage. I play everything on a 7, so it's not a case of I'm playing an Iron Maiden song so I'll switch basses. I like the fact that I can play 'regular' bass or play some chordal or solo stuff. To me it's just about having those choices on the instrument so I can play what I want, when I want to and playing whatever is suited to the music that I'm playing.
The ERB doesn't tell me what I should play, but what I could play.