Client wants to use the Carryover Balance (CB) as of 1/1/08 to cover all 2008 quarterlies - let's say the CB is $200,000 and each quarterly is $10,000 - if the employer makes no contributions in 2008 is the CB as of 1/1/09 just ($200,000 - A)*(1+i) where A is the sum of each quarterly amount discounted back to 1/1/08 at the effective rate i for 2008 ?

I'll take a stab. To simplify, I think you should do all 2008 calculations @ 1/1/2008. In the following 2008 CB is as of 1/1/2008, 2008 MRC is w/o regard to CB, and B is discounted minimum required residual contribution, so A+B = 2008 MRC:

2008 CB reflecting 4 quarterlies = $200,000 - A

2008 CB reflecting 2008 MRC & contribution = MIN(0, $200,000 - A - MIN(0,B - discounted 2008 contribs))

2008 PFB relecting 2008 MRC & contribution = MIN(0, discounted 2008 contributions - (A + B) )

2008 balances brought forward to 2009 using actual return on assets for 2008.