Matchless hotbox clone--->dual-channel options

[zaubertuba]

I'd like to build a dual-channel overdrive based on this Matchless Hotbox clone:

Matchless Hotbox : DIY Fever – Building my own guitars, amps and pedals

I want one channel for a light overdrive/bluesy rhythm breakup, and one that can be driven harder for more crunchy distortion/overdrive tones. And of course a true bypass (or alternately, buffered bypass, haven't decided yet) for a completely clean tone.

What's the best option to adapt this circuit?

a.) Add a gain control to V2a, and make it switchable.

b.) Add a tubescreamer-style clipping and gain stage ahead of the "clean" channel buffer.

c.) Add another tube for an additional gain stage (but perhaps a lower gain tube, like a 12AU7) on the "clean" channel, and perhaps a different tone stack for the heck of it, and a bypass, to make it a true dual-channel unit.

...or other options? Space isn't a concern because I'll likely rackmount this and design in a remote switch pedal.

Thanks in advance for your comments!