1. The hyperbola's equation:
\[ \frac{x^2}{4} - \frac{y^2}{9} = 1. \]
2. The chord's equation, parallel to \(y = 2x\):
\[ y = 2x + c. \]
3. Midpoint analysis: The midpoint adheres to the locus equation, derived by inserting \(y = 2x + c\) into the hyperbola's equation.
4. The simplified midpoint locus is:
\[ 9x - 8y = 0. \]