Practice one song until perfection, or many at once?

[Richter_Belmont]

Hello. This is my first post in the FFR boards, but I've been playing FFR itself for about a year now. I guess I could be considered one step above TOTAL NOOBDOM. I can play "Burnout" with all perfects except for about 10 goods, and maybe an average once in a while. I've played "Breaking the Common" without missing a step. I guess I can play songs with a STEADY stream of steps allright, I'll get better with practice.

My problem is, is that I cannot play even the most basic song if it has many, for lack of a better term, "double-hits'. I can handle one or two spread out in a song, but once many of them get mixed in with single hits at once, chaos ensues.

I've been practicing all the songs at once, and I've only seen inprovement in songs like the above. I know practice is key, but I just can't seem to get these types of songs. (Maybe CIA Rave is an OK example.)

For one, is it possible to really master these types of songs one-handed? Two, is it better to practice one song at a time till I get it rights, or should I practice many songs in one sitting to improve? I'm frustrated, I can almost perfect NEO-Max... except for the parts where about 25 steps appear in about 1.3 seconds...