The famous Armenian consonant shift did not in fact affect all PIE voiceless stops, but only those in word-initial position or after another obstruent, crosslinguistically the most favorable environments for aspiration. The remaining instances were then lenited to voiced fricatives, so that e.g.
PIE *t (> *[d]) > *[ð]. These then reverted to stops after sonorants (e.g. in mard, and*) and in pronominals (dow, -d), but *[ð] disappeared intervocalically, giving *(R), *y, or *w depending on the identity of the neighboring vowels.
Only for the position V r must a shift of *[ð] > *[B] be assumed, eventually producing new diphthongs in e.g. arawr, hawr.