You’re right, this particular clause would need extensive surgery to help a judge (or the judge’s law clerk) trace through the conditions. As an exercise, and to help me understand what the clause said, I took a stab at it below.

I don’t think putting the conditionals clause last would help much in this particular instance. I think you’d want the reader first to grasp the broad outline of the parties’ intent, then to drill down into the details. This suggests separating the definitional parentheticals and putting them later.

(I agree with you about the difficulties presented by “reasonable best efforts.)

For long clauses like this, I also like to put IF and THEN in capital letters (and sometimes underline them), as signposts for the reader.
Here’s a shot at the necessary surgery:

(A) This [clause] applies if:
    (1) Parent is not able to obtain any of the IRS Rulings and Opinions of Counsel, or
    (2) in obtaining the IRS Rulings and Opinions of Counsel:
        (i) the Parties would be required to make factual statements, representations and/or covenants that differ materially from the Representations and
        (ii) the differences in such factual statements, representations and/or covenants would reasonably be expected to result in the aggregate, in
          (X) a significant adverse effect on Parent and its Subsidiaries, taken as whole, on the one hand (a “Parent Adverse Impact”), or
          (Y) a significant adverse effect on the Company and its Subsidiaries, taken as a whole (a “Company Adverse Impact”).
(B) IF the circumstances described in (A) above come to pass, THEN Parent, Spinco and Company shall use their reasonable best efforts to restructure the Transactions in a manner that will accomplish the following:
   (1) preserve the economics of the Transactions to Parent, Spinco, Company, Parent Stockholders and Company Stockholders, and
   (2) result in the receipt of such rulings and opinions.
(C) Solely for purposes of determining whether the magnitude of an adverse effect on Parent and its Subsidiaries is “significant”:
   (1) Such effect shall be measured relative to the Spinco Entities only; and
   (2) Parent and its Subsidiaries (other than the Spinco Entities) shall be disregarded.
(D) Any determination whether the magnitude of an adverse effect on Company and its Subsidiaries is “significant” shall include, for example, due consideration of the effect on Company’s ability to take actions in the ordinary course of operating a radio station or radio network, such as, for example:
   (1) programming changes (including changes in format),
   (2) adoption and change of call signs,
   (3) contracts and other relationships with talent,
   (4) sales,
   (5) employment and labor matters,
   (6) capital expenditures,
   (7) ordinary-course acquisitions and dispositions of assets,
   (8) acquisitions for cash or debt, and
   (9) ordinary (i.e., non-equity-linked and not part of an investment unit) “straight” debt financing and refinancing as described in Section 1361 of the Code, but without regard to the identity of the borrower or the lender.