To put the £5m investment into context, the last set of accounts to end of season 11/12 also stated in the commentary, that a further circa £16m had been invested up to 30th Nov 2012, so that doesn't cover the entire season, and they can invest less than a third of that figure for next season.
If the owners gambled on promotion next season (so risk of transfer embargo 14/15 season if failed) and succeeded, they then have to pay the exact value of any spend in excess of the limit to the championship clubs (it would then be evenly shared between all clubs who complied to FFP).
However the club have indicated they will comply with FFP & if they don't mean by paying fines, then it has to mean big cuts in the wage bill and little spend on transfer fees, however don't forget all other clubs have the same issue, which is why clearing big salaries off the payroll isn't going to be easy, so could result in the need to sell those we can move on, even if its not the preferred option