From what I understand, the best letters of support will come from people in industry related to your proposal. But is that to say that academics with expertise in your area are not viable (I have heard mixed opinions on this)? For example, we have an academic expert as part of our Scientific Advisory Board — would this not provide a strong support letter as well?
It is best to provide a variety of background in your Letters of Support. Having an industry expert voice their support is generally good for supporting the commercial traction of your proposal/innovation. Having an academic expert voice their support for your innovation generally helps support the innovation section and technical description. Other popular angles for Letters include potential customers and beneficiaries.
One note on soliciting letters from your advisory board, while this may help express confidence in the scientific rationale behind the innovation, it may be perceived as lacking outside enthusiasm as that individual has already some degree of vested interest in your innovation. An outside academic expert would be preferred in this case.