I can definitely help you in this endeavor and you will have flawless results - trust me. I just took my dedicated root beer/ soda tap offline and converted 'er over to an extra beer line. I have used the Sprecher root beer,cream soda, the cola and the cherry cola (door county cherries no less!) and all are great.
I just typed through the entire process I went through to find out the perfect results in a thread earlier this week( see link below ) and had these sodas on tap for about 4 years. But I had 4 gallons of charged soda water sitting idle waiting for a gallon of syrup for over 6 months and thought heck I dont even use the soda tap or miss it anymore therefore the decision to switch it to beer.
See the following link:
viewtopic.php?f=4&t=106274
You will need to read between the lines as he was making syrup and I suggested right away to use Sprecher gallons.
And secondly just ignore some of the uber techie stuff towards the end of the thread if you need to as I kind of got side tracked and my thoughts then drifted to another topic altogether.
Although if you have questions regarding any part of the process just tack another thread back into this post.