[Advaita-l] Query about a passage from taittirIya AranyakaM

[Animesh]

SrI mAtre namaH , 

Namaste , 

While studying a vedic selection book ( named as 'Vedic Sanchayan' ) I came  across following passage of taittirIya AranyakaM ( 2nd prashna 10th anuvaka )
" 
पञ्च॒ वा ए॒ते म॑हाय॒ज्ञास्स॑त॒ति .............॒ यथ्स्वाध्या॒यमधी॑यी॒तैका॑मप्यृ॒चय्यँजु॒- स्साम॑ वा॒ तद्ब्र॑ह्मय॒ज्ञस्सन्ति॑ष्ठते॒ यदृ॒चोऽधी॑ते॒ पय॑सः॒ कूल्या॑ अस्य पि॒तॄन्थ्स्व॒धा अ॒भिव॑हन्ति॒ यद्यजू॑षि घृ॒तस्य॑ कूल्या॒ यथ्सामा॑नि॒ सोम॑ एभ्यः पवते॒ यदथ॑र्वाङ्गि॒रसो॒ मधोः कूल्या॒ यद्ब्राह्म॒णानी॑तिहा॒सान्पु॑रा॒णानि॒ कल्पा॒न्गाथा॑ नाराश॒॒सीर्मेद॑सः॒ कूल्या॑ अस्य पि॒तॄन्थ्स्व॒धा अ॒भिव॑हन्ति॒ यदृ॒चोऽधी॑ते॒ पय॑आहुतिभिरे॒व तद्दे॒वास्त॑र्पयति॒ यद्यजू॑षि घृ॒ताहु॑तिभि॒र्यथ्सामा॑नि॒ सोमा॑हुतिभि॒र्यदथ॑र्वाङ्गि॒रसो॒ मध्वा॑हुतिभि॒र्यद्ब्राह्म॒णानी॑तिहा॒सान्पु॑रा॒णानि॒ कल्पा॒न्गाथा॑ नाराश॒॒सीर्मे॑दाहु॒तिभि॑रे॒व तद्दे॒वास्त॑र्पयति॒ त ए॑नन्तृ॒प्ता आयु॑षा॒ तेज॑सा॒ वर्च॑सा श्रि॒या यश॑सा ब्रह्मवर्च॒सेना॒न्नाद्ये॑न च तर्पयन्ति "

The translation was " If one studies one rik , one yaju , one sAma , one atharvangirasa mantra one's forefathers are benefited from rivers of  milk , ghee , soma and honey ...... "  

My question is do this one one rik , one yaju , one sAma , one atharvangirasa mantra means first mantra of rigveda , yajurveda , samaveda , atharvan veda or any mantra belonging to respective veda samhitas ?
Do this phrase ' one rik etc ' is Upalakshan for any mantra of respective samhitA or it conveys meaning 'of the first mantra of all vedas '.

( generally people recite the first mantra of four vedas in bramhayagyaM )

Another thing it also mentions  benefit  of studying ' brAhman , ItihAsa, purAna , kalpA , gAthA , nAramshasi gAthA '.

But generally there is restriction on chanting of nAramshas gAthAs .
 taittrIya brAhman mentions "यद् ब्राह्मणः शमलमासीत | सा गाथा  नारशंस्य भवत् | यद् अन्नस्य | सा सुरा || ( taittirIya brAhman 1.3.2.6 )
"   
Also kAThaka samhitA mentions "गाथा अनृतं नाराशंसी मत्तस्य न प्रतिगृह्य अनृतं हि मत्तो यदा हि .........." ( kAThaka samhitA 14.5 ) 

Please clarify .


Regards 
Animesh