those arent rhyrthm lites those are the rhythm controls that weight like 1000grams + each get diff tires(dth works) a new frame, and your set for rear end weight
tires: maxxis dth seat: go pivotal, some of the federal seats look pretty good cranks: I'm not too sure. demolition medials, deity vendettas, redline device. something of that nature.(get better advice with the cranks )
That bike doesn't weigh 38lbs. I thought my Fire Eye weighed 33lbs when I weighed it on the bathroom scales, then I double checked using some much better scales I found in the garage and found its actually 26lbs. The quality of the scales really makes a difference lol
Right, now for the useful part. To make it lighter I would suggest lighter tyres, cranks, pedals, tubes, singlespeed, and maybe a lighter brake or no brakes at all.