Excel to act as background calculator in Salesforce

Desired Functionality / Process: 1. Input Fields are automatically or manually filled into a new custom Salesforce object 2. Press "Calculate" and all of the inputs are sent to an uploaded excell workbook and outputs are calculated 3. Output data is pushed back to Salesforce, populating the appropriate fields 4. (Optional) Desired Excel tabs can be converted to PDF, as defined in the Excel workbook print area, formatting, etc. Additional characteristics: - The end user cannot see the Excel spreadsheet during the whole process - Ideally able able to use Excel custom formulas, which requires saving as a "macro enabled" .xlsm workbook We are essentially looking to replicate the functionality of: (a) Apttus X-Author PRESTO product: http://x-author.com/custom-applications/ (b) CalcFusion product: http://calcfusion.com/en/features/ But instead of paying a 3rd party an ongoing SAAS fee, we would like to own the functionality ourselves.