Here's what you can do, noting that I must assume your accountant is correct given the fact that your accountant is more privy to your personal facts and circumstances than I:
If your company had a loan on the company books to you, the shareholder, then the company could deduct interest expense against the PSC tax rates. You in turn recognize interest income (ie... ordinary interest income) which can be offset by your investment interest expense on the SBA loan. Talk to your CPA.
I'm not going to say the above is the correct thing to do... If it's a business loan to you, then it should be a business loan (ie... deductible as a business expense). I'm personally upset by the PSC status when, at the same time, your loan is considered money used as an investment in a C-Corp, generally, as I said above, but that doesn't mean my personal feelings weigh over reality and the need to be objective. Also, if you put a loan on the C-Corp books as I hint, why does the C-Corp owe you? Microsoft would not owe you should you borrow money in your name to purchase its stock, so why is it any different if it's your company (ie... think ownership percentage and why this is your personal business and welfare as opposed to The Company's, or Microsoft's.).
The truth is that you invested in a company. You also work for that company. The tax code specifically states that interest on a business loan is different than interest on an investment loan, court case - smort case (which court?... this is not your specific case). Working for a company (employment) is not the same as making a business loan to that same company (investment, business loan if a schedule C... ok... hmmm...), and you're responsible for the loan then it sounds like, not the company, so it's no different than if I borrowed money on a credit card and bought stock...
There is no one easy answer.
Thank you for your question.