They complained and claimed that we would also have to use ROPE (a Microsoft link to SOAP) in order to get to their COM objects. The result of adding another two layers to the process would cause slow downs.

"It'll be too sloooooow" is a classic stalling technique. The way to deal with it is to force them to get specific.

• How fast do they need to it be?
• How many requests/second do they require, and with what latency.

Resist the temptation to get into a language pissing match until they answer these questions.

Once you have numbers, prototype and benchmark. Then prepare for the next objection. Rinse, lather, repeat.

Keep a list of the objections they raise, and how you counter those objections. That might come in useful if they give up raising objections in favor of just insisting you use their tools of choice.