I'd say that it could be useful, depending on your speakers. I've read some things that suggest that the RP-91 may actually have some bass management capability, but I don't know how extensive or if it works for the DVD-Audio. The 950 gives you the option of an 80Hz crossover for all five channels on the analog input, so if you think you'd get good results with that (all of your speakers would work well getting 80Hz on up, and your sub getting below 80Hz) that could be all you'd need. If you'll be using the DVD-Audio a lot and need better bass management than the 950's 80Hz crossover or whatever bass management the RP-91 offers, then you'd need the ICBM.

I'd recommend against getting an ICBM before you have a chance to try things out. See what settings you use on the 950 for your speakers (crossover frequencies and such for the 950's bass management) and see if you want similar settings on DVD-Audio -- if you can't get them with the RP-91 or 950, then I'd go after an ICBM.