Derivation of E9/B6 from the C6 Tuning
Most people start with E9 when attempting to describe how the E9/B6 Universal Tuning was designed.

Since I feel that it's actually closer to C6 than E9, I will begin by showing how one can lower the C6 tuning 1/2 step to the key of B and use a standard C6 pedal change (P6 in Fig. 1) to convert to E9.

Figure 1 shows the stock C6 tuning, as installed on most double-10 pedal steel guitars.  It consists of 10 strings, 5 pedals, and one knee lever.

Figure 2 shows the B6 Tuning, 1/2 step lower than the standard C6 Tuning -- our starting point.  Lets look at it carefully.  Figure 3 shows how the E9 tuning relates to our B6.
Pay particular attention to the arrows.  If we engage the E to D# knee lever on E9, it becomes clear that SEVEN OF THE TEN STRINGS OF THE STANDARD E9 TUNING ARE THERE.  We are missing the 2nd, 3rd, and 9th strings.  So far our tuning will require 13 strings.  Since there aren't many 13-string pedal steels available, we will probably need to settle for either 14 or 12.

My personal preference is to avoid 14 strings.  Lets shoot for 12, but we'll have to compromise and the most logical string to eliminate is the 9th string on E9.  If you examine the B6 tuning, you see that Pedal 6 gives us the note we need -- by lowering the E on the 8th string to D (same as the 9th string on standard E9).  Lets summarize what we have so far.
This tuning buys you virtually everything the two tunings on a stock 8 & 4 Double-10 will produce AND MORE.

The C6 Side of the Tuning
You can duplicate any of the chord voicings and single-string capabilities found on the C6 neck of a D-10.  THE ONLY DIFFERENCE IS IT'S 1/2 STEP LOWER.  All twelve strings are usable as an extended version of C6:  Strings 12 through 4 are identical to C6 strings 10 through 2.  The first string is the equivalent of a G on top of C6 and the third string is the equivalent of having a high A (sixth tone) on top.  Pedals 4-8 and the Left Knee Right are the standard changes usually found on an 8 and 4 Double-10.

C6 players like to raise A to Bb on their 4th (and often 8th) string(s).  The G# to A change on the B pedal duplicates this function.  Some players raise C to C# on the 3rd (and sometimes 7th) string(s).  Half-pedaling the A pedal makes that change.  Some lower A to Ab on 4th (and sometimes 8th) string(s).  The common E9 knee lever lowering G# to G will get that change.  Since the C to B knee lever is already on our tuning (B to Bb in B6), we have the equivalent of 4 C6 knee levers and all 5 pedals.

The E9 Side of the Tuning
The only deviation between the standard E9 and the tuning shown in Figure 4 is that the D usually found on String 9 is not as readily available (you have to use Pedal 5, so you can't combine it with the 'A' and 'B' pedals).  Some players may not find this to be a problem.  If you do, see Figure 5, below, for some additional changes that include two different ways to get the D, both of which allowing combinations with any pedals (both are on knee levers).  One of the real advantages of this tuning is that you get full chords in the lower register using the standard E9 pedals.  Figure 5 shows several other useful ideas for enhancing the tuning further.
Enhancement #1
Replace Pedal 6 (see Figure 4) with a Knee Lever
Rationale:  The reciprocal motion of RKL (used to form the B6 chord/tuning) and LKR is natural.  It is easy to let off of LKR while engaging RKL (and vice versa).  When you study the B6 tuning, it is clear that the chord produced by pressing Pedal 6 in Figure 4 is an E9.  The pedal supplies the lower b7 tone while raising the (already lowered) fourth string back from a D# to its rightful open tuning (an E).  This lever, on its own in an E9 context, also produces a nice low-voiced dominant 7 chord (e.g. strings 11-8).  It also produces a nice moving tone (tonic to b7) while the upper tonic (on 4) or lower tonic (on 11) remain the same.  This enhancement is most appropriate for someone who is not already accustomed to playing 10-string C6, and would be accustomed to finding this change on a pedal.  Obviously, eliminating this pedal creates an empty slot for you to fill with another change, if desired (Pedal 8 in Figure 5).

Enhancement #2
Add the Lower E to F# on the 'C' Pedal (Pedal 3)
Rationale:  This change is useful both to bridge the gap in the lower octave when playing scales and when using the B and C pedals as the root for a IIm chord.

Enhancement #3
Add the D# to C# Change on String 2 to the E to D# Lever
Rationale:  Many C6 players (e.g., Buddy Emmons) have been using a D on the top of C6 for several years.  This change gives the B6 equivalent on the second string, in addition to the equivalent of the older standard G (F# on the 1st string).  I have found that this change is very useful for the 'C6 Side' of the tuning and doesn't get in the way of the E9 usage.

Enhancement #4
Add the B to D Change on String 9 on the Lever that Moves the Second String
Rationale:  Gives the equivalent of strings 9, 8, 7 on E9.  This combination of notes is not available using Enhancement #1 (lowering the 8th String to D) and is used occasionally in licks that employ the 9th string on E9.  Using this change and the E to D change as appropriate can produce some possibilities not available on the standard E9 (and C6) tuning(s).

These are just a few ideas.  The possibilities are nearly limitless.  This tuning allows the player to really understand the functional relationship between two tunings that are thought to be so differnt that they warrant separate necks.

Did you notice the 'double duty' of the B to Bb knee lever?  (it is the standard C6 lever shown in Figure 1 AND is a very popular change used by many E9 players)

A lot of C6 players raise A to Bb -- that's actually the same function that the E9 'B' pedal performs (it's G# to A in B6)

What else can you find???????

You may want to check out some of the other features of the tuning that I use.

Write me if you have questions.