My logic behind the controller was well if the music slowed / beat dropped I could manually "control" the light and slow it down etc? Or is that not what a controller does? Sorry for all the questions!
No worries about the questions - that's what we're here to help with. So let me take a step back and try to explain a few things. I'll be making several generalizations for the purpose of simplicity, but here's the gist on a lot of this:
Many DJ lights can run in three modes - auto, sound active, and DMX. Auto mode just cycles through a series of pre-programmed chases or looks. Sometimes the speed of the cycling is adjustable. Sound-active mode cycles the light through (usually) the same set of programs but uses the bass in the music to trigger the cycles. Some lights will automatically black-out or transition to a static look if there's a lack of music...others won't. DMX mode foregoes all that for use with a DMX controller.
A DMX controller sends commands to light fixtures that translate into colors and movement from the fixtures. The "decoding" will vary by fixture but DMX is an industry standard. With any DMX controller you, the end user, will be required to program the various scenes, looks, and/or chases into the controller for playback during a show. You gain significant advantages by doing this over using the fixture's internal chases since you can program the lights to look and move exactly how you want, but it takes time and skill to get everything to come out right.
The DMX controller can then playback the chases either automatically at the rates/times you've preprogrammed, can (in some cases) use music input or an onboard microphone to trigger the same chases based on the music, or can be triggered manually by the operator to sync to the music as best determined. All professional operators use this last option or will have their lighting equipment triggered by timecode (or sometimes MIDI).
As mentioned in a previous post of mine, your expectations need to be very low to find sound-to-light triggering acceptable. It'll work, but it usually has a very random and erratic look to it. Your best bet is to program a variety of chases on a DMX controller and trigger them in real-time based on your music. This will require the most work on your part but will also look the best. If this is more scope than what you originally intended I vote to try the headphones and see what that looks like before spending more money. Good luck!