Hey Dante, you'll get some interaction in the box with the 2 speakers in it and the additional box cubic volume should help the bass.  But hey, you'll hear if you like it.

What he said 

Richard,

  It's interesting to see if it lives up to the hype. I'm also a fan of Jeff "Skunk" Baxter, who uses one of these for session work. He claims he just takes this and his guitar and plugs into the desk with it. I can see that with an engineer working you into a mix. I'm not really convinced at this point it would work beyond a certain point as a live fly rig.

Hey Harley, very interesting journey.  BTW I'm also a big Steve Stevens fan.

Hey Dante, you'll get some interaction in the box with the 2 speakers in it and the additional box cubic volume should help the bass.  But hey, you'll hear if you like it.

Hey Dante, this is very similar to how I've wired my spare slant split stack.  If you plug in just to the top jack (non-switching), you get both speakers mono, in parallel (so impedance will halve, i.e. 2 x 8 ohm = 4ohm etc.).  In this setup, when you plug into the switching jack (I just used the simple ones (3 lugs) which connect the tip to the middle lug with no jack and open when a jack is inserted but have there own middle solder lug which you'd connect to the other speakers +ve).  So when you also put a jack in this socket, the opening of the switch bit breaks the +ve to +ve connection (green wire) that's connected with no jack is inserted and will then be stereo (2 x 8ohms (you said)).  If you just plug into the switch jack, you just get the one speaker it's primarily/directly connected to. The slight difference using a normal 3 lug switching jack to the way MJMP does it with "cliff" jacks, is they have 4 lugs open/close both +ve and -ve connections (with jack plugged in, as in diagram) where the more simple switch jack just open/closes one lug (which you use for +ve to the other speaker (green wire) and the earth is connected (the way I did it) by the metal jack plate that both jacks are mounted to and in contact with.  So the red wire in the diagram (-ve) is not needed (the way I have it) as it's connection is provided by them both being earthed/connected to the metal mounting plate (or you need to wire the 2 jacks earth lugs together if they are mounted on plastic etc.). The 4 lug cliff jack method is better, but both work.

Simple way for you though would be wire it stereo and use your cab merger when you want mono.

Wow, if you wanna see some people bickering online, just do a search for Two 1x12s vs One 2x12 and you'll get people ready to fight 

Whatever, I'm hoping I get a slightly larger sound from one 2x12 cab. I've been using two 1x12s for a few years now, I'm used to it. When I take the 2x12 to practice, I'll be able to tell. I even put the same exact two speakers in the 2x12 that I've been running in my 1x12s. I switched out one if the 1x12 speakers with my trusty EV Force.

My theory is two people yelling in the same room would be louder than two people yelling in separate rooms, mixed together    I don't know if it'll work, but I don't wanna fight about it

I saw that diagram Kim, but I don't understand it....forgive me

Dante, didn't I already had you covered back earlier in this thread?   

Here's another one I recently used to reconfigure one of my cabs.   This original post has been edited to use the Cliff jacks MJMP mentioned below.
 


This uses a switching jack to make the 2x12 Stereo or Mono depending on whether both jacks are uses or just one.  Here, the other non-switching jack is the Primary jack.  Plugging into the Primary jack alone gives a Mono 2x12 at 8 ohms (each speaker is 16 ohms itself).  Adding another plug to the Switch jack splits the 2x12 into Stereo at 16 ohms per side.  Note that plugging into just the non-switching jack alone will result in just one active speaker at 16 ohms.   

Be sure to clearly label the jacks as to which one is the Primary and be sure to match the impedances to your amp in regards to which jack(s) you will be using.

Harley,
That's what I was thinking, except for the shunting part.

I figured the simplest way was just to wire each speaker to a jack, boom - stereo cab. I have two jacks in the cab with the wires soldered to the jacks, tied up inside to do that if I want.
 
Right now it's a mono 16 ohm cab, which is perfect for my lunchbox heads. I still have my two 1x12 cabs for running stereo.

Okay, an update on this set up so far.

I've been doing a lot of experimenting with this GP-10 and trying different ways of combining guitar and synth sounds. I'm really not too impressed with just going with the 13-pin connection.

It seems the best sonic blends I'm getting are using the guitar jack to a dedicated amp, and the synth effects into its own system. This means a separate stereo amp and speakers for the GP-10, with the blend switch on the guitar set to synth only. You can use the "both" position on this switch, but I find that the V-guitar tones will often drown out the synth tones behind it. Plus, when you mix that V-guitar with your guitar tones coming from your amp, it sounds weird. This isn't really going to cut it IMHO as far as a fly rig goes. Apparently, I'd need to bring an extra power amp and speakers for the synth sounds. That's the kind of rig I expect to use with the GR-55.

As a straight up effects pedal, bypassing any synth effects, it gives you the Boss quality type of effects you'd expect. Not bad, but nothing spectacular. For that matter, I could run it through the effects loop of my rigs. I haven't tried that yet, but that's next.