A company is not going to make exceptions or negotiate special terms for a single employee, that would be a bad precedent and make the company messy and unfundable. That doesn't mean all is lost. As a key early employee you would have some options.

Vesting acceleration upon acquisition. If there is already a "double trigger" acceleration clause for some founders or employees, you should argue that you deserve that too. If not, tell them they should create that provision and you deserve it. And if you are one of the first hires, before they even have an option plan, you can offer to help them shape the terms - you might even have more experience and outrank the founders or be a semi-founder yourself, so your input could be useful to shape the compensation plan.

Double trigger means that your unvested equity (typically a portion of it, say 50%) immediately vests if you are fired in connection with a change of control. The fairness argument is that if you've helped the company get to the point of an acquisition you should share in the proceeds, whether or not they keep you around after. If they just dumped you after you did all that work, they're taking unfair advantage of your efforts. It's a switch they can turn on and off, and you can argue that it should be on for you.

You can't reasonably get full acceleration, or acceleration on an acquisition in which you are not fired. The reason is that the acquiring company needs to give you an incentive to stay and remain loyal. If you are due millions of dollars whether you stay or go, it is in your best interest to go. But 50% double trigger vesting is quite common.

FYI, the only people that would routinely get 100% acceleration upon a change of control / liquidity event are board members and advisors. The theory is that if they get the company to that point they've done their job in full. As an employee, no. They still need you to perform to help with the integration and start the acquiring company off in the right direction.

Protection against liquidation preferences. You're not going to get this one because the founders and seed investors don't have it. Liquidation preferences are one of the terms the investors cram down on everyone else because they can, and because they do want to protect their investment. As you note, they mean that the investors get their money out before anyone else... well, before any other equity investors. Secured debt holders and taxing authorities come first, and then unsecured debt (such as your salary), and then preferred investors. Then everyone else.

You're also not going to get anti-dillution protection either, while I'm at it, or a long-term contract with severance pay. You're on the same boat as the founders here.

If you're thinking fairness, it's only fair. If the company gets sold for less than the investors put in, no value has actually been created. Why do you or the founders deserve to take home some cash as a reward for losing the investors' money?

Keep in mind that provisions like "participating preferred", discounts, or liquidation multiples that allow investors to double-dip are not too popular anymore. The investors usually get their money back, _or_ a share of the sales proceeds, not both. So the liquidation preference comes into play only as a backstop to return as much of the investors' money as possible, not a way for investors to get rich at others' expense.

Some things you might be able to negotiate instead... make sure you have a full 3 months to exercise your options, not a shortened period. No good leaver / bad leaver provisions. Your stock or options should continue to vest as long as you have any relationship with the company, not just as an employee. See if they'll agree upfront to allow a "net issuance exercise" or a loan to purchase the option shares, because otherwise most employees can't afford or don't bother exercising their options when they leave. Like the vesting acceleration, don't expect to get a special term nobody else gets. But if they do have these sweeteners available in their plan already, or if you're helping them set up a plan in the first place, it's reasonable to try to include them.