Hi:
Thanks for the questions regarding the T7 and T6 preamps.
The price of the T7 in the SL chassis is $1199. The T7 page shows the EC version, but the price list shows all of the possible configurations. For example, the phono stage for a T7 is a $299 option (either chassis).
The T6 is a fine preamp. It significantly outperforms our older FetValve preamp, tube preamps (3i and 4i) and solid state preamps. The T6 has a very nice soundstage that is extremely accurate and dynamic. With the new lower price it's a very good deal.
The T7 was born from the older FetValve preamp. In developing the T6 (and the T5) we did some pretty serious engineering, to get the most transparent sound possible. With the T7 we took some of the engineering ideas from the T6 (and T5) and applied them to the FET Valve design and the result is the new T7. The T7 expands on the dynamics, opens the sound, and delivers the most accurate reproduction we have ever made.
We currently offer an OmegaStar phase inverter that can be factory installed in the T6 and T7. You can use the phase inverter to get the balanced output, but there is no room to add the bigger jacks. When installing the phase inverter we have the non-inverted output on the Output 1 jacks, and the inverted output on the Output 2 jacks. How long of interconnect do you need to run?
As for building the kit, that's a personal preference. I believe the shipping charges are around $15. The checkout time on the bench is free, however. I would not want to build the kit if your only objective is to save the money as it's a pretty hefty project. I suggest the kit only if you enjoy building electronics. My first experience with AVA (long before I started working with them) was an Omega III preamp kit and I very much enjoyed the project, but I'll admit kits are not for everyone.
Thanks for your interest in AVA products!
Larry Jenkins