Lots of coy responses to the 'soundboard quality' statement. Honestly, the reason for these responses is that tapers generally feel that the best audience recording at a live show sounds better than the best SBD recording. SBD's are usually very stale and the mix is often bad, but mainly the SBD recording loses the 'feel' of a live show. My personal opinion is the best sounding live recordings are a matrix between a well mixed SBD and a good sounding AUD.
But yeah there's so much involved with getting the best quality recordings from the audience. This has to do mostly with technique and microphone placement...as the saying goes, it's all about location, location, location. But if you want SBD quality, the most important factor...even more important than the quality of your mics, is getting your mics in the right spot in the venue. That also means minimizing the audience, without eliminating them altogether. Mics mounted on your body are usually too close to other audience members and their talking or applause will be too distracting. So the better solution is to get your microphones several feet above the heads of audience members on a mic stand in order to put the audience sounds into the background of the recording. There's so much more to talk about mic placement, but that the basics. As far as high end gear, here's a start for you to consider.
Microphones:
Schoeps Capsules > Schoeps active cables or Custom cables (available from schoepnbox on this board)...most start with a pair of MK4 cardioid cables or perhaps MK4V. You also can't go wrong starting with MK41 hypercardioid capsules. The cables and capsules will run you around $2000 USD on the used market.
or
DPA small diaphragm series...such as DPA-4022 (there are currently a used pair in the yard sale for $2500 USD). These microphones come with the cables integrated with the microphones.
Preamps:
Many to choose from, but most portable battery powered preamps that people prefer on taperssection are no longer in production. A couple of options for preamps at the low and high end that are currently still in production are...
nbox manufactured by schoepsnbox, the same maker of the cables mentioned earlier. This is a very small preamp that is ideal for pairing with a Sony M10 recorder. Around $500 to $550 USD.
Schoeps VMS5U, much larger full featured portable preamp. $2300 USD.
Recorder:
Many many to choose from. You need to decide whether you want to use small handheld recorder or a full featured recorder. The quality of sound you get from either is the same...the more expensive recorders are buying additional features...more channels, etc. Recorder will cost you anywhere from $200 USD to several thousand.
Misc gear:
When you budget for your rig, you'll also need to include at lest several hundred additional dollars for items like gear bags, cables, clamps, mic stand, mic mounts, wind screens, rechargeable batteries, and so on.
Leave you wallet at the door. Many people with high end rigs have more than $10K worth of gear.