Before you go spending a bunch of money on new amps and other expensive options, check whether you have impedance matching issues. Unless your amp has a very high impedance input level, your problem with "not sounding like an upright bass" and your volume problem are probably both due to impedance mismatching. The Gage pickup on the Eminance, at least, is 3MΩ Many bass amps don't work well at that level.
It's a cheap option to try. Fdeck's got one for $55 including shipping.
http://personalpages.tds.net/~fdeck/bass/hpfpre.htm
Then if that doesn't help you can look at more expensive or more time-consuming options.
But try the simpler cheaper stuff first.