Why do you say that the Hx60 would be an expensive muffler in a compound arrangement? I really disagree with that notion. Like you said, Cummins guys use them in high power compounds but I have also seen it on some moderately built Cummins as well. Even what is considered a high powered IDI, we still run relatively low boost numbers compared to a Cummins. But at the same time an IDI needs more CFMs than a Cummins due to the cubic inch difference. So consequently, an IDI can run decently sized compounds and still be able to spool them. But the other side of that equation would be fuel. IMO you would need at least 150cc IP and roughly 40psi from a set of compounds to even be worth it. Both Justins ran around 40psi with a single and the engines seemed to hold up pretty well. There are also a few more guys that will be running that kind of boost soon as well. It should be pretty interesting.
Oh and one more thing, I agree that an Hx60 is slightly large but with enough fuel it could spool. It would be a bit harder to drive as a DD and I'm sure it would be smokey and hot. Compounds would definitely be the way to go if you wanna use it...