Since "drive" really is a term that came from an amplifiers ability to deal with complex and difficult impedances from loudspeakers it really doesn't apply the same to preamps.  A preamp only has to drive an easy load with very little impedance or impedance that changes very little might be a better way to phrase it.  

"Drive" in a preamp really comes from it's voltage swing, the larger the swing, the more drive.  Our CSP3 for example has up to 30 volts of potential output with a 2 volt input which is perceived as "drive" when listening because the music is well animated and dynamic.  

So there is no reason to create a push pull preamp to create a sense of drive, when it can be easily done single ended.