I was going to post this question and my response on my web page. Would you like me to include your name/contact information?
I must admit that I haven't used the MPX 1 extensively with the bass guitar but I think you'll find it an awesome addition to your rig.
I should point out that I tend to build programs from the ground up rather than starting from a preset. This works for me because I know so much about the box but it may not be a good approach for new users. You should probably spend some time just trying out each of the presets, making a list of those that are interesting to you.
The MPX 1 can do a lot of different things, so how you use it can vary quite a bit. The few times I've used the MPX 1 with a bass guitar I always found myself loading an EQ effect to fill out the sound. The EQ on the bass amp I use is quite limited but the MPX 1 EQs allowes me to fatten up the sound quite nicely.
The MPX 1 is like a constructor set but only a limited number of pieces will fit together at one time so you have to plan you program carefully. Each MPX 1 program consists of effects blocks which are connected internally but each effect you load uses program resources. If you don't need EQ therefore, don't waste the resources on it. The Pitch effects are the heavy hitters for program resources so use them carefully.
One of the things to keep in mind is that program loads on the MPX 1 are not instantanious. Loads can take up to a second depending on what effects are included. Reverbs and delays are the worst. If you need a fast program change, don't use reverb or delay (delay might not be as bad). People who own the R1 remote often create programs with multiple effects which DO toggle on and off instantiously.
For someone who is going to be using the MPX 1 extensively, I'd also recommend spending some time just trying out each of the effect algorithms. Load the "Blank Slate" program and add effects to it.
Two of the most important aspects of the MPX 1 are the Patching system and the internal controllers. The Patching system in the MPX 1 is basically a machine that allows a control source of some kind to change a parameter in an effect block. For example, if you wanted to control the reverb "mix" parameter via the gas pedal on your R1, you would create a Patch with the pedal as the source and the Reverb "Mix" parameter as the destination.
Sources can be internal or external. The R1 gas pedal is an external control source. The MPX 1 has an amazing arsenal of built in controllers however. These can be used to control virtually all of the parameters in the box. Definitely check out the patching system and internal controllers.
You can actually create a compressor in an MPX 1 program by using one of the internal "Envelope" controllers to control the master output level or the Level parameter on one of the effects. You could even make a mulitband compressor if you encorporate an EQ effect.
One very useful effect in the MPX 1 for bass is the MOD effect "Overdrive". This combined with EQ, DELAY and/or REVERB can produce some awesome effects. Another favorite of mine is the PITCH "Sweep Filter" effect which is essentially a moog filter. Check out the "EkoSweepFilter" program (#78 on the V1.0 ROM).
One thing to watch out for on the pitch shifter programs is the fairly long delay that they add. I'm pretty sure that its a bug that was fixed when it was ported to the MPX G2 but pitch shifts on the MPX 1 have around 100ms of delay that can be very aggravating.
I could go on and on but need to cut it short.
I hope this all helps. - Bob Sellon