May be I do not understand the question. NIntegrate handles vector and matrix integrands. This is what I get with the table C2 at the end of the notebook in the original message:
In[16]:= NIntegrate[C2, {\[Xi], 0, 1}]
Out[16]= {{0., 1.}, {5., 0.99994}, {10., 0.999877}, {15.,
0.999813}, {20., 0.999747}, {25., 0.999679}, {30., 0.999609}, {35.,
0.999537}, {40., 0.999464}, {45., 0.999388}, {50., 0.999311}, {55.,
0.999232}, {60., 0.999151}, {65., 0.999068}, {70., 0.998983}, {75.,
0.998896}, {80., 0.998807}, {85., 0.998717}, {90., 0.998624}, {95.,
0.99853}, {100., 0.998434}, {105., 0.998336}, {110.,
0.998236}, {115., 0.998134}, {120., 0.998031}, {125.,
0.997925}, {130., 0.997818}, {135., 0.997709}, {140.,
0.997598}, {145., 0.997485}, {150., 0.99737}, {155.,
0.997253}, {160., 0.997135}, {165., 0.997014}, {170.,
0.996892}, {175., 0.996768}, {180., 0.996642}, {185.,
0.996514}, {190., 0.996384}, {195., 0.996253}, {200.,
0.996119}, {205., 0.995984}, {210., 0.995847}, {215.,
0.995708}, {220., 0.995567}, {225., 0.995424}, {230.,
0.99528}, {235., 0.995133}, {240., 0.994985}, {245.,
0.994835}, {250., 0.994683}, {255., 0.994529}, {260.,
0.994373}, {265., 0.994216}, {270., 0.994056}, {275.,
0.993895}, {280., 0.993732}, {285., 0.993567}, {290.,
0.993401}, {295., 0.993232}, {300., 0.993061}, {305.,
0.992889}, {310., 0.992715}, {315., 0.992539}, {320.,
0.992361}, {325., 0.992182}, {330., 0.992}, {335., 0.991817}, {340.,
0.991632}, {345., 0.991445}, {350., 0.991256}, {355.,
0.991065}, {360., 0.990873}, {365., 0.990678}, {370.,
0.990482}, {375., 0.990284}, {380., 0.990084}, {385.,
0.989883}, {390., 0.989679}, {395., 0.989474}, {400.,
0.989267}, {405., 0.989058}, {410., 0.988847}, {415.,
0.988635}, {420., 0.98842}, {425., 0.988204}, {430.,
0.987986}, {435., 0.987766}, {440., 0.987544}, {445.,
0.987321}, {450., 0.987096}, {455., 0.986869}, {460.,
0.98664}, {465., 0.986409}, {470., 0.986176}, {475.,
0.985942}, {480., 0.985706}, {485., 0.985468}, {490.,
0.985228}, {495., 0.984987}, {500., 0.984743}, {505.,
0.984498}, {510., 0.984251}, {515., 0.984002}, {520.,
0.983752}, {525., 0.983499}, {530., 0.983245}, {535.,
0.982989}, {540., 0.982731}, {545., 0.982472}, {550.,
0.982211}, {555., 0.981947}, {560., 0.981682}, {565.,
0.981416}, {570., 0.981147}, {575., 0.980877}, {580.,
0.980605}, {585., 0.980331}, {590., 0.980055}, {595.,
0.979778}, {600., 0.979499}, {605., 0.979218}, {610.,
0.978935}, {615., 0.978651}, {620., 0.978364}, {625.,
0.978076}, {630., 0.977786}, {635., 0.977495}, {640.,
0.977201}, {645., 0.976906}, {650., 0.976609}, {655.,
0.976311}, {660., 0.97601}, {665., 0.975708}, {670.,
0.975404}, {675., 0.975098}, {680., 0.974791}, {685.,
0.974481}, {690., 0.97417}, {695., 0.973858}, {700.,
0.973543}, {705., 0.973227}, {710., 0.972909}, {715.,
0.972589}, {720., 0.972268}, {725., 0.971944}, {730.,
0.971619}, {735., 0.971293}, {740., 0.970964}, {745.,
0.970634}, {750., 0.970302}, {755., 0.969968}, {760.,
0.969633}, {765., 0.969295}, {770., 0.968956}, {775.,
0.968616}, {780., 0.968273}, {785., 0.967929}, {790.,
0.967583}, {795., 0.967236}, {800., 0.966887}, {805.,
0.966536}, {810., 0.966183}, {815., 0.965828}, {820.,
0.965472}, {825., 0.965114}, {830., 0.964755}, {835.,
0.964393}, {840., 0.96403}, {845., 0.963665}, {850.,
0.963299}, {855., 0.962931}, {860., 0.962561}, {865.,
0.962189}, {870., 0.961816}, {875., 0.961441}, {880.,
0.961064}, {885., 0.960686}, {890., 0.960306}, {895.,
0.959924}, {900., 0.95954}, {905., 0.959155}, {910.,
0.958768}, {915., 0.958379}, {920., 0.957989}, {925.,
0.957597}, {930., 0.957204}, {935., 0.956808}, {940.,
0.956411}, {945., 0.956013}, {950., 0.955612}, {955.,
0.95521}, {960., 0.954806}, {965., 0.954401}, {970.,
0.953994}, {975., 0.953585}, {980., 0.953175}, {985.,
0.952763}, {990., 0.952349}, {995., 0.951933}, {1000., 0.951516}}