The Onyx Preamps are excellent, and while the rest of the board
is pretty basic, you really don't need anything but the preamps to
get a good clean signal to the recorder. ( I don't know if the board
uses an analog or digital connection to the SDR, which could potentially
compromise the signal... ) Depending on the instrumentation and size
of the band it sounds like you have enough microphones that are suitable
to the standard four piece band. You might consider a JDI direct box
for the bass, even if you mic the cabinet, because it is better suited to
the job than the Mackie DI on the board. Use the shortest cable runs
you can, make sure your cables are of similar quality. Plan out instrument
placement for best separation and isolation ( assuming you cut the basic
tracks live) and you should be able to get very good results that you can
take to a studio with better mixing capabilities and be happy with the results.
Two things to keep in mind. One, even though you may plan on just doing
guide vocals in the tracking session, be careful to set it up and record it as
if they were the final vocal overdub, and also spend the time getting the
sound you want with mic placement, as that is a huge time saver later.
( Not having to pay someone else to compensate for lack luster tone.)
That means check to test recording on speakers as well as headphones
if you can. Best of luck to you.

Thanks for the advise.
I have used that set up as you have described and I'm happy with the results, but it would be nice to hear someone do it better than me and then show me what they done. All this trial and error stuff can really take time. I'm not affraid of hard work and effort, but I don't like flogging a dead horse.
Main problem is not having a control room in the areas that I'm recording in. Trying to guess a good sound is almost impossible and listening back in an untreated room is pretty tricky too.
I managed to get a really good drum sound on one of my recordings but came home and listened to a song and it made mine sound so amatuer. What I need is hours, days, weeks of try this and try that.
I have bought my lottery ticket, I'll let you know how I get on...

Hello,
I am happy to pass on what I can.
Two additional thoughts, if you are tracking in an untreated room,
it can be helpful to have good pair of 'open back' headphones to check
the tracks with. You will want to used closed phones when tracking, but
as they enhance the bass and tighten up space, you won't get a accurate
impression of the raw recording.
The other thing, which may seem obvious, but in my experience is often
a problem, is the musicians are not prepared. To get the best recording,
everyone one needs to know their parts and have their instruments in tune.
While individual instruments may sound great on their own, do they conflict
with each other for the same spot in the sonic landscape? If the arrangement,
performance or instruments are off, then the whole recording will be off.
I agree that there is no getting around spending hours and hours learning,
this is something that you never get past, as you never can learn enough.
There was a great quote in "Tape Op' once, ( I forget who made it now... )
but the engineer said it and the essence was; "At any given point, every person
in the room feels like it will be discovered that they have no idea what their doing"
You know something that works two days in a row can suddenly sound awful
without any component having changed. All that being said, a poor recording
of a great song played with heart will always trump a highly polished track
that is devoid of soul. Best of luck.