I don't really know from which process this "professional fullnes" comes (probably from both) but there is something on these songs that my home recordings lack.
That would mainly be a good solid bass, but there is something else that just makes them "full and round"..
Did you use a lot saturation plugins/analog gear?
i'll share what i can about the recording process
Guitar: Fender mexican strat on bridge humber - peavey jsx - 2x12 cab with vintage 30s - 2 57's one into Gap pre73 straight on cab, other into solo 610 fredman style quite a bit lower in the blend processing was high and low pass filter, 0.1 db of mid range with waves hls and a bit more mid range with the chandler tg stuff.
Bass: Fender American Jazz bass - passive JDI - GAP pre 73 - Pro tools sansamp plugin. processing was waves ssl comp, wavs ssl EQ plus wavs pultec thats about it.
Drum shells are all samples except Hitoribocchi intro and outro (snare part) thats mostly the real snare HIGHLY PROCESSED. samples of kick and toms are from superior drummer and snare is brady oak from ssd mixed with another slate snare. cymbals were recorded with studio projects c4 rooms are u87/tlm 103 M/S on 3 of the songs and 414s b-uls in blumelin these are both CRUSHEDDDDDDDDDDD and distorted to oblivion and back then some really big reverb on them and very very low in the mix.
Vocals: lead is u87 in solo 610 processed with sound toys decapitator, waves la2a then 1176 all buttons in mode cranked, waves api and chandler tg EQ backing vocals are into a 414 i switched comps and pre's for each song haha processing just softube cl1b. screams are mostly into 414 but some are into a n sm7b either into gap pre or vintech 573. distorted wit decapitator and compressed to oblivion with 1176.
mastering is a hair of chandler tg eq ssl comp and two fab filter pro L's one limiting second one cliping A HELL OF A LOT.
Fab filter stuff is the best thing ever.
The only advice i can share to getting this sound is have really tight players that know their songs and use decent gear and know the sound you want. Hope that helps!