None of the mp3 players require soundcard. All can play with paula directly or through AHI (AHI comes with paula.audio device). OK, there might be some excceptions like MAS-player's own software or delfmpeg, but those should be obvious needing the decoder hardware.
I've been using AMPlifier for over ten years as my main mp3-player. For some years with paula and it worked pretty well with it when you had 060. If you gave it bit higher priority than default is, then it played without any cuts no matter how much you used other programs and CPU.
Then I got Delfina Lite soundcard and AMPlifier worked fine with it decoding mp3:s with its DSP. No CPU load at all.
And nowadays I'm using it on MorphOS with Pegasos.
So, I'd say it's pretty compatible program and if it doesn't work, it's probably an user error. And actually if you don't have soundcard with hw decoder for mp3, then using soundcard needs more CPU power than paula.
About mail and news combo... I wouldn't try to find combo. Separate programs are better for separate jobs, IMHO

YAM or SimpleMail is good for email and I guess there's some news programs too.. at least NewsRog and NewsCoaster seem to be open source nowadays. I had successfull test with NewsRog long time ago... I myself don't use mail or news locally, so can't say anything sure about those as main programs. I use Pine and Tin on my mail server.