Welcome to the board Nathan.
The quick answer is it will work fine but like always there is more to the story.
As long are your first stage is working properly, there is no real performance gain to be had by replacing it but depending on your second stage design, upgrading it may be a step up. With the exception of a rare few regs, pretty much all reg use an intermediate pressure (IP) of 135-145 PSI so your choice of second stages is broad, as long as the second stage is rated for an IP in that range, any second stage will work. All Aqualung regs (except some very old US Diver ones) are rated for 135-145 psi. The issues come in service and initial installation. At least here in the US, most shops carry a few brands and will only service those. If you choose a different brand of reg for your second stage and your preferred service shop does not service both, you can have problems getting the complete reg serviced. The next issue is for best performance, the second stage needs to be tuned or adjusted to work best with the first stage. Since both the first and second stage have an acceptable range of working pressures, if the first stage happened to be adjusted to one end of the range while the second stage is adjusted at the other, you will not get the best performance out of them or possibly the second stage will free flow. This is not a compatibility issue, just one of tuning them to work together. If your other stages are due for service, this is not an issue (assuming your shops works on both brands) because adjusting the stages to work together is part of the service. If it not up for service and you buy from a local shop, I would think they would be willing to adjust it for you.....or you can learn to do it yourself but that is a little more involved.
