This sentence presents some problems regarding the syntactic analysis, especially with the period "..., é só isso."
Three possibilities were considered:

1) Coordination at the clause level

Assuming that the comma would work as a coordinating conjunction, then we would have a compound unit with two conjoints being finite clauses.
However, if this option is acceptable strictly in syntactic terms, it clearly does not satisfy semantics.

2) Coordination at the subclause level

This possibility would coordinate two accusative clauses. Something similar to:

(2.1) Penso que o fundamental é que "Where in the world é o primeiro álbum mesmo "da banda", (penso que) é só isso.

The direct object would be a compound unit, with two conjoints as finite clauses.

3) Finite subclause attached to the whole previous period

The above sentence is similar to:

(3.1) Penso que o fundamental é só isso, é que Where in the world é o primeiro álbum mesmo "da banda"

So, the demonstrative pronoun isso would refer to the whole previous period in the sentence, almost acquiring a relative meaning.
Because there isn't still the option of having a clause predication (hypothetically @#FS-S<PRED), the solution would be the following:
 

Penso  [pensar] <fmc> V PR 1S IND VFIN @FMV
que  [que] KS @SUB @#FS-<ACC
o  [o] <artd> DET M S @>N
fundamental  [fundamental] ADJ M S @SUBJ>
é  [ser] V PR 3S IND VFIN @FMV
que  [que] KS @SUB @#FS-<SC
$"«
Where=In=The=World  [Where=In=The=World]  PROP M S @SUBJ>
é  [ser] V PR 3S IND VFIN @FMV
o  [o] <artd> DET M S @>N
primeiro  [primeiro] <NUM-ord> ADJ M S @>N
álbum  [álbum] N M S @<SC
mesmo  [mesmo] <ident> DET M S @N<
$"«
de  [de]  <sam-> PRP @N<
a  [a] <-sam> <artd> DET F S @>N
banda  [banda]  N F S @P<
$"»
$,
é  [ser] <fmc> V PR 3S IND VFIN @FMV @#FS-S<
só  [só] ADV @>N
isso  [isso] <dem> SPEC M S @<SC
$.

4) Chunks of discourse

According to the criteria for sentence separation that was established, the comma is never a sentence separation marker. Therefore, the sentence was not divided although it is clear that there are two different, separate chunks of discourse, despite the anaphoric reference (isso). A sentence separation mark, like the full stop or semi-colon could actually replace the comma in this context.
The analysis found for this sentence was considering the top node as a compound unit, but instead of conjoints (CJT) one would have statements which are finite clauses (STA:fcl):

A1
STA:cu
<sic>R. -- </sic>
STA:fcl
=P:v-fin(PR 1S IND) Penso
=ACC:fcl
==SUB:conj-s que
==SUBJ:np
===>N:art(M S) o
===H:adj(M S) fundamental
==P:v-fin(PR 3S IND) é
==SC:fcl
===SUB:conj-s que
==="«
===SUBJ:prop(M S) Where_In_The_World
===P:v-fin(PR 3S IND) é
===SC:np
====>N:art(M S) o
====>N:adj(<NUM-ord> M S) primeiro
====H:n(M S) álbum
====N<:pron-det(<ident> M S) mesmo
===="«
====N<:pp
=====H:prp(<sam->) de
=====P<:np
======>N:art(<-sam> F S) a
======H:n(F S) banda
==="»
,
STA:fcl
=P:v-fin(PR 3S IND) é
=ADVL:adv só
=SC:pron-indp(<dem> M S) isso
.
 

The same case applies to sentence  C176-2, see graphic tree: