ASM is not cutting voltage to the DRL or the Ignition as they are feed from there own fused circuits. Using the tach output is a interesting idea but point less if the ASM isnt capable of supply the coils the current they need on a consistent bases
I think it's important to confirm that the ASM is not able to supply enough current to the coils. This should be easy to test. I would use a volt meter to measure the difference between the ASM orange wire and the ASM pink wire. If the ASM is not able to supply enough current, you should see several volts of difference between these two signals
when the bike is running. Can you do this test?
The other thing I was thinking was that it would be nice to rule out some oddball issue with the DRL-400. This seems unlikely, but maybe it's triggering early? Maybe some kind of noise? In any case, is the DRL-400 wired in a way that you could disconnect it and still run the Dyna 2000?
Those two tests are what I'd do first. It doesn't require anything other than a volt meter and some time. If the volt meter test shows a large voltage drop across the ASM then you can install a relay and provide full power tot the coils. A mechanical relay might not really hold up, and I don't know how fast they switch so it might add some delay, but it would certainly allow you to test the ASM without requiring it to supply the full coil current.
If you want to try a relay, I'd start with this one:
www.mouser.com/ProductDetail/TE-Connecti...2F5x5Mx1xziJ5Q%3D%3D
The turn on time is 7ms, and the off time 2ms. That seems pretty good. It has two output terminals, so you can run a wire for each coil. The relay activation coil only draws about 0.17A so the ASM should easily drive that.