• To install Fixed Quantities for Grouped Products, please follow our generic installation instructions
• To enable the extension, go to 'System> Configuration>Catalog' navigate to a tab available called "Blue Jalappeno Fixed Quantities', set 'Enabled' To Yes and save
• Install Tiered Pricing Across Multiple Products as per instructions and configure

Configuration 

1. Edit the grouped product under Catalog > Manage Products and set "Enable Fixed Quantities" to Yes 

For each child simple product:

1. Edit the product under Catalog > Manage Products and set up tier prices, these must be the same for every child product within the grouped product
2. On the Inventory tab, set 'Enable Qty Increments' to Yes, set Qty Increments to the desired quantity e.g. 6
3. Set maximum qty allowed in shopping cart to desired max quantity e.g 144
4. On the Prices tab, set Cross Tier ID to value for the grouped product, this value must be set on all products

The quantity increments value will determine the step between quantity available for purchase for each individual product. The maximum qty value will determine the maximum displayed quantity in the drop down. The quantities used in your tier prices will determine the total quantities available for purchase for the grouped product.