You have a variety of choices. I would start with 4th generation SHARCs. The 2147x is the least expensive and adequate for Dolby and many biquads. If you use the 100 pin parts and a large enough power supply, you could also use a pin compatible ADSP-2148x for more MIPs. I don't think you will need the 2148x unless you have a lot of additional processing requirements.
There are software libraries available that are Dolby certified from ADI. If you are high volume, perhaps the ROM versions might be an alternative. Regardless, you will need Dolby licenses to move very far forward.
Sigma Studio for SHARC is available. You might also want to check out DSP Concepts Audio Weaver. I believe they have some Dolby experience. Navigating Dolby licensing is probably harder than implementing the code. I would start by talking to some of the ADI audio segment specific support people. I'm sure some of the ADI application engineers who monitor this list can point you privately to someone. If not, I can help. I am not invisible, google my name and send me an email.
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Al Clark
www.danvillesignal.com