chess:
for DIY, a passive DI box is practically the easiest and most useful thing you can build. buy a jensen transformer that has one winding at about 50k ohms and the other winding at about 600 ohms. on the 50k side, connect one terminal to the tip/hot of the unbalanced source(1/4 jack). the other terminal is connected of the ground of the DI housing and to the ground of the source. connect one terminal of the 600 side to the hot on the balanced output(XLR jack), connect the other terminal to the cold of the balanced output. connect the ground of the XLR jack to the ground of the housing. if you want to get fancy, put a switch that will interrupt the path from the XLR to the ground. there you have it, it is that easy.