There are a number of new exotic mosses available that I've seen on Aquabid lately. Pellia is a nice one that has a nice star pattern that doesn't get as stringy as Java moss. I have no experience keeping it (yet) so I don't know how easy it is to care for. Alternatives to Java moss are christmas or tiawan moss which are bushier, brighter green, and more compact. There is also a mini-moss that has very compact growth, too. Weeping or willow moss is also like java fern, but has bushier fronds that tend to grow in a downward fashion, and peacock moss is very similar, except that it grows upward and can be very attractive waving in the currents or the wake of that lovely arowana you've got.
With any moss or liverwort, regular trimming will be necessary, especially if you have bight lights and/or CO2. You'd be amazed at how quickly this stuff can cover a piece of wood even of the size you've got. Also, regular trimmings will encourage denser, bushier growth. An easy way to tie on lots of moss and get good coverage is to use nylon hair nets instead of fishing line or thread. It creats a grid over the wood, and then you just weave the moss in, but it's nearly invisible otherwise. Moss also tends to trap all kinds of debris, and with a big predator, there's not many critters you can keep to keep it clean. Amano shrimp work great, but would probably get eaten in no time. So you'll have to do it manually. When you do water changes, try to siphon through the moss, or take a turkey baster and shoot water into the moss to loosen debris.
With any moss or liverwort, regular trimming will be necessary, especially if you have bight lights and/or CO2. You'd be amazed at how quickly this stuff can cover a piece of wood even of the size you've got. Also, regular trimmings will encourage denser, bushier growth. An easy way to tie on lots of moss and get good coverage is to use nylon hair nets instead of fishing line or thread. It creats a grid over the wood, and then you just weave the moss in, but it's nearly invisible otherwise. Moss also tends to trap all kinds of debris, and with a big predator, there's not many critters you can keep to keep it clean. Amano shrimp work great, but would probably get eaten in no time. So you'll have to do it manually. When you do water changes, try to siphon through the moss, or take a turkey baster and shoot water into the moss to loosen debris.