what is the easiest way to get more rear travel out of my 2001 srx 700

The rear shock should be adjustable on that. Stiffen the shock if you're bottoming out. If you've got 8" of travel, and your body weight is compressing the shock down to 6" of travel, then stiffening the shock will give you an extra inch. If you want to go up and down like an elevator, buy an aftermarket suspension. But remember, if you end up raising your rear end, it will affect your handling on corners when you're trail riding. You may end up having to get a ski widening kit, and raise your front end up and inch or so to compensate for the rear end being lifted. You may also be able to get an aftermarket shock that has an extra inch or so of travel.
Also, try playing with your front limiter strap. When a sled goes airborne the entire undercarriage moves forward, then back again as you make contact with the ground. Sometimes tightening your limiter strap a hole or two will stiffen up the rear end a bit, as it prevents the undercarriage from moving as far forward. Less front to back movement only leaves the suspension one option.....more up and down movement.

Well adding travel is not going to be easy. Your SRX has the short travel Pro-Action skid. Yamaha thought the faster sled did not need the 11 1/2 inches the other sleds had. To get more useable travel you will need a bunch of parts from the long travel skid. Or you can optimize what travel you have currently by making sure the transfer rods are set correctly for your weight. If you start letting out the front limiter strap you might have a real problem steering the sled. Basically with the strap out the sled will understeer or not steer at all. What you might want to do is get an adjutable transfer rod from Bender or others. Stiffer springs are offered if you are a bit heavy and it bottoms out too much for you. There is also an adjustment on the rear shock to adjust for soft or stiff.

Cranking up the preload on the center spring (the one that is in the front of the skid) has a tendency of breaking the W arm. Check out Maxx Perf they have kits that might help you.

Maxximum Performance and Pioneer Performance both offer long travel kits for that sled. Send in your shocks and they take them apart and put in the longer shafts from the long travel skid. They also replace the center spring. As part of the package, they rebuild and recalibrate the shocks to your wieght and riding style. You also get new limiter straps and control rod spacers. Put it back together and off you go. I did this on my 1999SX600 and it made a huge difference in ride quality. It costs about $400 but well worth it. The shocks are set up so there is only a slight increase in ride height so it does not affect handling nor does it require a long travel front. Check their web sites for details. Your other option would be to buy a used Viper (or other) skid. I've seen them for $350 - $400 range but you never know how beat up the components are.

i had the same problem with clearnce on my srx and im a big guy i tryed to adjust the mono shock and couldnt get enough clearnce so i bought an m-10 suspension and i have all kinds of clearnce its great now i love that suspension but it does come with a price tag but in my eyes it worth the money.