I had one for use with my old dub band. Here's the only pic left of my board at that time:
God I miss that band and that board. One of my all time favorite collections of pedals. The open spot was soon filled by a Turbo Rat which sounds awesome blended. But I digress.
I used the Deep Impact for bouncy synth tones and it was perfect for the job.
To me the major synth pedals all sort of have their own vibe. The DI is very 80s/90's synth stuff with a bounce to it. The Korg G5 is great for the vocal filters and is perfect for G Funk type hip-hop sounds. The EHX BMS does 70's prog rock synth sounds and the Octavius Squeezer does more modern, hard edged synth sounds.
If I want the sounds of the AKAI there's really nothing that cops them. The G5 covers some similar ground with the Markbass probably being the closest thing in terms of a substitute. But I just didn't dig the MB. Partly the interface, partly the fact that I don't think you can drop out the clean signal but for whatever other reason it didn't click with me. But worth trying out for sure.
I can't say I miss the Deep Impact because there's no call for it in what I currently do (post-rock band and an infancy stages Thievery Corporation styled project) which is why I sold it but it's great for what it does.
As far as replacing it, I do cop some electronica tones using the tried and true octaver, fuzz, filter/LP filter sweeps with other pedals added for modulation.