You should really try to continue seeing a doctor to have them taper you off. I know that it is expensive, but it may be cheaper than your hospital bills would be if you seize from the withdrawal. Valium is a lot better to use for tapering, which is another reason why continuing to see a doctor is a good idea. The following advice is for if you don't see a doctor and try to work with what you have;
Tapering is always easiest in the beginning while you still have a larger amount of the drug in your system. See how low you can go in the beginning by taking just enough to get by. Sleep will be a big issue, so stay away from anything stimulating (caffeine, energy drinks, etc) an OTC antihistamine to help with this. Diphenhydramine is common, as is doxylamine, and along with being a good sleep aid, they may help with anxiety a bit.
I think that you can get that 4-6mgs down to 3mgs pretty easily. It's really tough to taper with xanax due to its short half-life, so something like whit grapefruit juice may help drag out the duration of the drug a bit. The best and most basic advice is to take as little xanax as possible, and I generally try to save my main dose for the night in order to help sleep.
Alternating days with the lowered dose has helped me transition to the lower dose. So lets say that you are at 4mgs, aiming to get down to 3.5 mg, (I think that .5 every 2 weeks is more reasonable until you get down to 1-2mgs in which I suggest lowering it every 3 weeks) I would do so by alternating days on 4mg and 3.5mg. So Sunday, 4mg, Mon, 3.5, Tues, 4mg, Wed, 3.5, Thurs, 4, and then 3.5 from then on until you wish to lower down to 3mgs.
How often do you take 4mgs as opposed to the 6mgs? If you mostly take the 6mgs, then alternate days with 6 and 5mgs until stabilizing at 5, and then do the same with 5 and 4, and then 4 and 3, and then from there you should only drop by .5 instead of 1.
I know that my posts have kinda been all over the place and some of the stuff is kind of conflicting, but any further advice will require knowing your current pattern of use a little better.
By the way, I was prescribed 3mgs of xanax for 4+ years before I tapered down to 1mg xanax, then switched to valium to taper, and now I take 1mg of valium daily. I figured I would mention that so you know I have personal experience with this.