After the range and volume of the solo are determined, you can focus on the timbre (tone color) of the solo.
HIGH-VOLUME solos can be achieved through strong solo reeds alone, or chorus reeds with the support of principals and mixtures, or possibly the full principal chorus.
Example 1: Swell Trompette 8' & Basson 16'
Example 2: Same as ex. 1, plus Mixture
Example 3: Same as ex. 2, plus full flue chorus
Example 4: Great full foundations through the mixture (possibly coupled to the Swell accompaniment)