The brass is stock Kontakt 5. 
Sunny Day was used because the “before” version was indeed “nearly there” as far as I was concerned. It could have stood on its own, but I was able to get a bit more room in it at least in my opinion.
Now let’s consider something more extreme. For the Musicians For Haiti project, Glyn, Wim, Peter and I did a song called Hunger. It was recorded in 2010, originally using a live bass and lot more reverb. I eventually replaced the bass with Scarbee and reduced the mix level of the reverb to something more manageable, and that’s what you’ll hear in the “before” version. I remixed and mastered this song to get something that sounds an order of magnitude better, in my opinion.
My inexperience as an engineer is reflected in the before version. 
I was going for a James Brown feel with this song, which the drums reflect and Glyn delivered on wonderfully.
Changes made during remixing:
Drum kit was changed from Multi-mic room to Tight Kit (Battery 3 → 4)
Added high shelf on the vocal group channel
Added SoundToys LittleMicroshift on the backing vocals group to thicken them up. This group gets routed to the vocal group.
Used stock track presents on the individual drum tracks. For those not familiar with how I record, a MIDI track holds the master drums, which I then render to individual audio tracks using the MIDI Transformer insert.
Removed reverb entirely from the master bus (in addition to removing the other inserts).
Added reverb to the lead vocal and drums group track
Added slight delay to the lead vocal and Wim’s tenor sax solo
Adjusted volume automation on a few tracks
Then I did the mastering process.