AI mixers and Series III mixers are not compatible, as they belong to two different "stages" of AVB networking. A RM / RML32AI could be a digital stagebox for you. You need to get the AVB option card for your console. As you probably can buy the stagebox and the card used/second hand, this might be a good option for you. The stagebox can also be used as independent rack mixer. Do NOT buy a RM / RML16AI, because that would limit your inputs to 16 and outputs to 8 (plus Main L/R and Mono). AVB first generation does not allow using two stage boxes.