Since you are planning on eventually getting a second panel, I'd avoid paying more for a special controller that can step-up the lower-voltage input. By the way, you mentioned the MX60. My understanding is that while it handles a large range of input voltages, it can only step the voltage down to match the battery and can't step a voltage up. The product spec, for example, states "Can charge a lower voltage battery from a higher voltage PV array" but doesn't say anything about stepping the voltage up. (It has a very low end voltage it can take, but that is because it can be configured to charge 12v batteries.)
Something to look into is making a buck/boost converter. This would sit between the panel and the charge controller and, in your case, double the DC voltage. Be aware that it does this by cutting the amperage in half, so it doesn't provide any magical boost in overall power. For example, if a 2:1 boost converter had 24v 10A input, it would have, not counting conversion inefficiency, a 48v 5A output. The advantage of the boost converter is that you'd be able to get a normal 48v charge controller without having to buy a second panel. The disadvantage (as there is no free lunch) is that there will be a conversion power loss. Depending upon the converter, you might lose up to 10-15% of the power. Some purists would object over losing that much expensive solar power, but in my view being able to use 85+% of the panel's output now beats not being able to use any of its output until a second, expensive, panel is purchased.
There is plenty of info on this site about building converters, so a search of the site might be a useful thing for you to do.
