See answers below:
1. Many people use amp distortion. Particularly in higher gain
applications, a boost, overdrive, or distortion pedal before the amp
input does not raise the volume rather, only increases gain,
compression, and noise. Most effects loops in quality tube amps are
line level only and unless the loop in question has the ability to run
at instrument level, drive pedals will not work correctly when placed
there. To accomplish a volume boost only in a line level effects loop
without any other changes in tone requires a device that either
attenuates the signal for rhythms and can switch to unity gain, giving a
perceived volume boost (i.e. low impedance volume pedal), or an active
device that can attenuate/boost such as the functionality added to the
latest TimeFactor software update.
2. The only other delay pedal that I am aware of that can handle
line level signals and can store volume levels on a preset basis is the forthcoming
Strymon Timeline.
3. With a range of -20dBu to +6dBu, the preset
volume control on the TF has the capability to do much more than simply
balance levels between bypassed and effected states.
4. I
absolutely could toggle between two of the exact same presets with
varying volumes however, it would require in certain cases to bank up or
down plus selecting the preset to get there. When it's solo time, it
would be far more convenient to have a single switch that is volume boost only. The number of presets available isn't the
issue. Plus, I have a free switch on my 3 button auxiliary foot
switch. 
