I play 4, 5 and 6 string basses.
The four is my old 72 Fender P bass. Learned on it many years ago and still my go to bass for blues. Roy does use a 4 string for the TMBG lessons, but he certainly does not only play a 4 stringer.
My 5 string is a 35" scale, MTD fretless and that is quite a different critter, but I love the sound and feel of a solid B string. Right, there are only four more notes below a 4 string, but it is so easy to drop down to a solid low D or even a thundering C if necessary. I don't go down there often during a song, but do use it for effect at appropriate points in a song (often near the end or the climax point in the song).
My 6 string is a Tobias Killer B and the upper C string adds highs that are available by just walking across the neck instead of pivoting or sliding up the neck. With extended range basses it is important to make sure that the pickups are set properly to get a similar volume from each string.
As far as the lessons go, you can play things on the middle four strings, just like Roy does in the lessons, but you need to extend the range of your scales, arpeggios, and chord work to include the upper and lower strings.
Both my MTD and the Tobias have Michael Tobias' asymetrical shaped necks, so they are thinner on the treble side and are therefore very easy to play in spite of the width of the necks, but still difficult to reach across and play the low B string above the 12th fret (but there are many options for playing those same notes elsewhere on the neck that its not an issue).
Extended string basses are not terribly difficult to play, but do give you a wider palate of places to play. If you want the mid neck tone, you can play the entire piece up there and that can be more difficult with only 4 strings.
Last edited by TobiasMan; 05-12-2011 at 06:09 PM.
Steinberger NXT5 EUB, MTD 535 Fretless, Tobias Killer B6, 72 Fender Precision
Eden WT500, WTX1000N & WP100, QSC PL230
Eden D410XLT, D410XST, 215, Fender Bassman 10