There is a lot here and it is difficult to address all the various issues you raised.
1) If the plan is being terminated, you should have been given a lot more than "a page to sign". You should have received a benefit election package which detailed your options on the distribution. Assuming the amount of your lump sum is > $5,000, it would have explained your monthly annuity options, as well as your lump sum option. It should have also provided tax information related to the distribution, and spousal consent forms.
2) You have the right to request a benefit calculation worksheet that details your benefit amount.
3) You have a right to a Summary Plan Description that explains how the the plan works and the benefits are determined. This should also define how any excess assets are allocated.
4) Regarding the allocation of the excess assets, they must be allocated in a non-discriminatory manor. Discrimination in this setting only looks at Highly Compensated Employees (owner) vs. Non-Highly Compensated Employees. (These are defined terms under the law.) Because the testing for a cash balance plan is typically done by looking at the benefits paid at Normal Retirement Age, older people often get more than younger people because younger people have longer for the money to accumulate. Often the allocation is done based on age and compensation. Older & higher paid get more $, younger & lower paid get less $.
If you have a 65 year old making $200,000 and a 25 year old making $20,000. The plan can give $50,000 to the 65 year old and $191 to the 25 year old and that would not be discriminatory because each would receive 25% of pay at 65, assuming 8.5% interest. 191 * 1.085 ^ 40 = 5000/20000 = .25 50,000/200,000 = .25. This is just an example to illustrate the point that younger people will likely get less. The actual allocation is often more complex, but this illustrates the method.