And probably much more economical to buy RS68s...
Aren't they the engines that they recently discovered would get destroyed due to the heat from the SRBs if used in a Shuttle type stack? Hence why Nasa is looking into making them regeneratively cooled for Ares V (yet more cost and time to develop). I can't remember the reasoning behind Ares V not just going back to SSMEs off hand. Doubt price is much of a factor.
I don't like getting into the technical aspects of things because as I said, I'm not educated in that field, but I thought I'd respond since that's what I've picked up from reading and you quoted me. If someone else is more knowledgeable in this area, please correct me if I'm going wrong somewhere.
EDIT - just thought I'd add, for completeness' sake, that DIRECT v2 involved using RS68s rather than SSMEs, but the above problem with them necessitated a change to SSMEs again, since when they've spoken with PWR about making expendable versions, and it seems viable, and cheaper.