Well, you can't do chases on the dimmer and do DMX control at the same time. The chase programs are designed for quick and easy light shows with minimal involvement. I like to use that for rotating between 4 party-type fixtures where I don't really care what is doing what when. For these party-type ligts(high tech FX), they need 100% on or 100% off. Cans let you get away with the variable output. With the latest batches of the DP-DMX20L, you can set your channels to switched vs dimming per channel, which is a great helper. I think there may even be an option to adjust power output either globably or per channel. Either way, this doesn't resolve the chase issue.
There are I think 2 modes in these. Sorry, I only ever use them in DMX mode. I think it's DMX mode and chase mode. It's an either/or thing.
And you're right, even in the slowest speeds, it's going to stil chase, just at a rather lenthy interval.
So, you have choices. I think there are compact sized programmable controllers, to rack mount controllers of various sizes and capability, or you could jump up to software control. I think, based on what I'm getting from you, one of the entry level controllers would be more than sufficient, so I would recommend the DMX Operator.
Other than that, maybe you can find someone who would do custom programming for your dimmer's chase chip. But, at 20% brightness? Maybe just go 100% and use lower wattage bulbs?