You have to be pretty innovative to build an entire business from one product niche as Network Computing Devices Inc does with its X Window System display terminals, and the Mountain View company is demonstrating the kind of innovation that will be needed to keep it ahead of the pack. Yesterday it launched its first multimedia X terminals – units able to produce sound as well as text and graphics. The new Modular Color X terminal line is built around the 88100 RISC from Motorola Inc and is designed to bring to mid-cost products functions and performance once available only on high-end units, including PEX three-dimensional graphics and a speed of 100,000 Xstones. The X terminals are the MCX14, a 14 with VGA or 1,024 by 768-pixel resolution at $3,300; the 15 MCX15 with the same resolution at $3,500; and the MCX17 17 unit with VGA, 1,024 by 768 or 1,152 by 900 resolution at $4,300. The MCX1 is a $2,300 base-only product that supports standard VGA and Super VGA multisync monitors, including high-resolution 1M-pixel monitors at up to 75Hz. All MCX units have 12 square base and offer compact disk-quality 16-bit sound with sampling rates up to 50KHz. Input devices range from microphones that go into the external jack to compact disk players; output can be throught the internal speaker, or via stereo speakers or headphones plugged into the speaker jack.