You haven't made 0 progress. You've spent the past half year noticing, taking an active interest and oberving them (how else would you notice they are sleep deprived). There are 3 approaches you can take
The first is just mustering the courage and not caring if you are a nuisance and talk to them regularly. What is it about the cellist that makes you want to befriend and talk with them? Use that as your basis to come up with topics to talk about, for example, if they are really good when they play, you can ask them about their routine. If he's sleep deprived, you could ask him how come he always appears so tired? If you can figure out what topics the cellist is interested in talking about, this will be rewarding and you'll be on your way to making friends with them. It's just a matter of trial and error (which is why courage and not caring if you are a nuiscance are key since you'll need to be persistent).
The 2nd method is to ask others in the orchestra to help facilitate a chance to talk with them. Does the cellist have other members they seem to talk to. That person could be your guide, maybe even give you pointers on what to talk about or about the cellist's personality that can help you succeed in your desire to converse with him.
The 3rd method is start small, for example, after an intensive practice, you could give him a bottle of water or something to drink and complement his efforts (if this is how you feel). If you do this regularly, you can expand the things you talk about gradually and you'll also become an existence on his radar.
Whatever you decide to do, the most important tip is to be brave and make a sincere effort. Even if it doesn't work out the first time, you can use the experience to decide what to do differently in future encounters. Just like how you decide to talk to us here, it's not that different with the asian cellist you want to get to know