I think the Soundwave-Cassette tandem went to Blackout-Scorponok+Frenzy.
Actually, the cassettes's roles were summed up and distributed to both Scorponok and Frenzy.
Soundwave and Blackout are both:
1. Big and Powerful. If you leave out the combiners, Soundwave is probably the biggest Decepticon next to Megatron.
2. Expert in interfacing with other computer devices.
3. Silent and does not speak much. Relatively, that is, compared to the screen time of each.
4. Emotionless and merciless.
5. Blackout's powerful EMP hints at his dominion over communication and electronic devices.
6. Smart and cunning. Attack from behind tactic.
7. Ever loyal to Megatron.
Scorponok & Frenzy's similarities to the cassettes:
1. Both are obviously ejected from a larger host.
2. Both are tasked to pursue and attack humans.
3. Frenzy as spy and inflitrator.
4. Scorponok, i believe can double as infiltrator as well, in some situations, with his ability to barrow into the ground.