software

i am about to change the preamp tubes on both my Marshall TSL601 COMBO and my Boogie dc5....The TSL has 4 12AX7 tubes V1,V2,V3,V4 and the DC-5 has six of them(V1,V2,V3,V4,V5,V6). I think i'll buy some JJ and some EH so i can mix them up and see how they sound that way. What i would like to know is do i need to buy some balanced 12AX7 for the phase inverter position(???) and which is the position for the phase inverter tube for each of the amps i mentioned earlier?

Yeah should buy balanced tubes for the phase inverter other wise the sound coming out my sound weird. The phase inverter tube is the closest to the power tubes.

Matched PI tubes are recommended... iff'n you don't you could get asymmetrical power stage disortion, which some people endorse. I would do it, though. The PI is usually, in my experience, the last stage before the power tubes. That would be V4 and V6, respectively.