Hi Toshiaki,
I use D'Addario Chromes on all but my Lotus/Steinberger bass, although different gauges. On my Exploiter I use D'Addario ECB80SL XL Chromes, Super Light Gauge (.040 .060 .075 .095) for the main four. I order GHS Singles (DYB-20, DYB-25, DYB-35, DYB-45) from JustStrings.com for the top four. I use Super Light Gauges because I want the least amount of tension on the neck. Flats are generally not as bright sounding as round-wounds but they hold their tonal qualities much longer since the fingers aren't constantly filing off skin and oil that builds up in the grooves of round-wounds. The top four ARE round-wound and provide plenty of high/bright tones. I've never been a daily player and over the years I've progressed (regressed?) from round to ground to flat-wounds. I'm not a Pro Player as I'm sure you are, but I love the sound. Finger playing has a nice warm/full sound but using a pick brings out the highs that cuts through everything! I hope this helps.
Thanks for viewing,
Lloyd