I wish I could help you more but so far I have not had a problem with range and my I ask why you want to run more volts in your TX. I do have a 6 volt 2500 MAh battery I run that cost about $15 shipped. If you get a React here is a coupon to get a free temperature sensor.
http://www.nomadio.net/nrp/coupon.php?code=9878ff17