That amp should be enough to drive you out of the car unless there is something very non-standard about it.

The RioCar player has (nominal) 4 volt outputs, which should be enough to drive any normal amplifier.

If that Infinity ampliifier has even 25 watts per channel, that should be enough output to drive the stock speakers unless it some really weird amp requiring higher input voltages, but I've never heard of such a thing.

Dumb question, but I'll ask anyway: Is there a gain control on the amp itself (there should be) and if so, is it cranked up high enough? You want to set it so that the player is as loud as you ever want to hear it with the player set to 0 dB.

The RioCar player's pre-amp output (line-out) is three to four times as "hot" as a typical CD player. If you are not getting adequate volume, then the problem almost certainly lies elsewhere (assuming the player is not somehow defective).

tantaafl.