This unit is comprised of four identical direct boxes in a 1RU enclosure. On the front, each DI channel has buttons for +20 dB boost, phase (polarity) reverse, 8 kHz high-cut, and ground lift. The buttons are LED-backlit when engaged. Phase reverse is always dimly lit to give you frame of reference in the dark. Each channel also has an eight- segment LED level meter. The XLR outputs are transformer- balanced. The back has XLR balanced inputs, 1/4'' unbalanced inputs, link outputs (a split of the input signal), and two -20 dB pad buttons (unlit) per channel. The case is metal. The power supply is internal.
I got this unit to record a dry and effected track from two guitarists at once. Neither of the guitarists complained that it changed their sound or interfered with their playing-a major triumph. Every time I've tried this with passive DI boxes, there are obvious differences in tone, and the guitarists say it changes the feel of their rig. There might be a downside though; a hum on the guitars was interactive. Guitar #1 would hum in the balanced output when both guitars were plugged in-but not alone. Guitar #2 would hum by itself-but not when #1 was plugged in. It made me wonder if I should have gotten separate boxes, but then they all might have hummed. In a different session, I used one channel for the piezo pickup on an upright bass. There was plenty of low-end thunder on the signal (and I had to cut some when mixing). I used the 20 dB boost, and it was clean.
The DI4000 can take up to 3000 Watts from an amp's speaker output with both pads engaged. My friend tried this with his mid-70's Fender Princeton. We were a little nervous because the manual doesn't say how it loads the amp. It didn't fry the amp, but it sounded like poop. It was very clippy in a way I can't imagine being useful to anyone. Then we hooked the link output to the speaker (the manual doesn't say to do this) of the Princeton just to see if it would work. The speaker sounded great. Too bad the direct amp part didn't work, or it would be a good trick.
My only serious complaint is that the outputs are on the front and the inputs are on the rear. Why?!? I have to cable from the front to the back of my rack to record, and I have to crawl around the back of my rack to plug in the instruments. Also, despite the tough exterior, the unit is made to be disposable. I couldn't fix a button I broke because the circuit board was glued in place.
Overall, the DI4000 is a bargain and yields great results. You'll really have to impress me to get me to spend more money on recording guitars direct! ($99.99 MSRP; www.behringer.com)