I wouldn't get fancy with any money you'll need in less than a year. Just stick it in a savings account, regardless of the low interest rate. You know you have a debt payable to the IRS in just 8 months. Investments in my experience tend to need a 2-3 year time frame to work out on average.
Look at it this way. Even though that money is technically the IRS's, you still get to earn a little bit of interest on the "float" until April. That's still not so bad.
Mike