Double MIDI input?

I have a very interesting problem on my hands. Here is the setup:

I have:

- Synthesizer

- Weighted Keyboard-Controller

- Surface Controller

- Computer

- Set of Speakers

And it is connected togeher like this:

Keyboard-Controller-->Synth-->Computer-->Speakers

Now the problem is I want the Controller Surface to also control the Synth. Both the Keyboard Controller and the Surface Controller are MIDI based and as most of you know there is only 1 MIDI INPUT on any given Synth or device in general.

NEW DIAGRAM

(Keyboard-Controller + Surface Controller)-->Synth-->Computer-->Speakers

I have tried having a simple volume controller (non-MIDI) hooked up to the Keyboard Controller, but then there is a time lag between when it fiddle with controls and when the Synthesizer responds (since it has to go through another device).

Would splitting the MIDI cable work and have 2 MIDI devices hooked up to 1 MIDI INPUT port? Or will that cause chaos? I haven't bought the Surface Controller yet, so I can't try it out. Any help, advice or predictions to how this could work?

I'm not 100% but you would need to have two midi inputs into your computer in order to do that. Having 2 MIDI devices hooked up to 1 MIDI INPUT port would as you said cause chaos.

Keyboard-Controller-->Synth-->Computer-->Speakers

I don't understand - what is the computer doing? Is it recording the synth or is it playing back the synth via midi? Why would you need a surface controller going to a synth?

If you are using a midi synth then you can let the computer control it. Notice in the below configuration you need two midi mergers to have two separate midi inputs, one for the synth (inputs from the keyboard controller and computer), and one for the computer (inputes from the surface controller and the synth)

............................................------->

Keyboard controller ----> Synth <------- Computer <------ Surface controller

Regardless- a midi merger should do the trick. There are also a number of midi router type devices out there.