Short answer: don't. Long answer: I have a USKOC and tried several PS2 to USB adapters. The issue isn't only on the input lag, but also on the low polling rates of the adapter.

• Beatmania Iidx Pc

Most USB adapters are so slow reading data from the controllers that when playing a game with so many inputs per second like Beatmania IIDX, it just can't read them fast enough. This results in button presses not registering, sticky scratch (scratch-heavy charts are out), and generally terrible gameplay. You're way better buying the cheapest USB keyboard that allows the most key presses at the same time. I tried out super dual box, super joybox, and inpin and the inpin adapter seemed to have the least trouble and input latency, but it was still noticeable, and im not sure if the inpin adapter is available anymore. I got used to it and got by with it for a while. I think it was around the time i hit 7th dan in iidx that i was finally able to afford my DAO PEe 2nd.

Beatmania Iidx Pc

I'd definitely try and take advantage of the dao has for the fp7 but that probably wont last long Lunatic Rave 2 has more lenient timing windows and better KOC with usb adapter support than IIDX, so I would probably just stick with that if you dont have access to any IIDX CS games on ps2.