Where To Tie In

I'm working on a project in Central Arizona and will be connecting to APS. The project will consist of a 250 kw solar field now and another 250 kw field in the future. The problem I'm having is where to tie into the existing electrical service.

The existing main switchboard is rated 4000 amps at 120/208V, 3 phase, 4 wire. There is no main breaker but instead there are 6 disconnects. The 6 disconnects prevent me from doing a service side tap as it would be the 7th disconnect.

The ratings of the six disconnects and what they feed are as follows:

200A - elevator
200A - elevator
400A - Panel
1200A - Distribution panel inside building
1200A - Distribution panel inside building
1200A - ATS which feeds a Distribution panel in the building

The ATS is outside and near where the inverter will be located.

My question is where should I tie in? I don't want to do it at the ATS as it may violate its UL listing. Also the lugs can't handle that many conductors. Can I intercept the feed coming to the ATS and put in a new distribution board and then refeed the ATS from it as well as tie into the inverter at the new board? Any other options?