The bottom lenses are x2 and x4, and with the original eyepieces result in 20x and 40x (10x times 2x = 20x)
With the 5x eyepiece and the 2x lens, it would result in a 10x, which should be pretty usable and in the middle of my B&L range. I have a StereoZoom 4, which zooms from 0.7x to 4x, plus a 10x eyepiece, which would make it 7x to 40x, but with the Barlow lens becomes a 3.5x to 20x. I do mpos of the work around 10x, so you should be in range, and rarely I need 20x when I'm dealing with a particularly fine pitch chip (but as I said, at that magnification the depth of field is really limited: you can have either the soldering pad or the top of the pin in focus, no both at once, and you need to pre-position the soldering iron tip before looking into the eyepiece
A zoom microscope is preferred when possible, since you have infinite settings between min and max, but your microscope with a 5x WF (don't forget the WF part) should be pretty good for most soldering work, and IMHO much better than any digital microscope. Given it's a relatively cheap investment to find out, I would highly recommend to get the 5x WF eyepieces
You can then contact Amscope and see if they sell 1x and 3x lenses, which would give you all the possible ranges you need. Actually, if you could remove the 4x lens, I would try completely removing it. At he end of he day, a 1x lens is nothing more than a glass disk to prevent dust from entering the microscope body, so removing the 4x lens and using a 10x eyepiece would give you 10x with your existing eyepiece. Then with the 2x lens and a 5x eyepiece, and 5x with no lens, you'd have every range you need (5x and 10x)