Help with first cable upgrade.

I have a Musical Fidelity v-150, rotel rp-3000 turntable and an old Sony CD player.  I have 2 sets of speakers B&W CM2's and JM Lab chorus floorstanding speakers I may have to part with due to space.  My power cables and interconnect cables are cheap stock.  My speaker cables are a 20 year old or so set of MIT shotgun cables.  Any recommendations for budget friendly cables that may help the bass or soften the brightness of my system?  Thanks.
Espace musical Muse 1 rca (andré the sorcerer)
Western electric hp (1950)
O2A Quintessence (sector cable)

Nice system. Consider Transparent Audio (TA) cabling. This brand is a sonic match for your gear. I used to own B&W/Rotel and Sony components with TA Super MM2 series interconnects / speaker cables.

Happy Listening!
It is a nice system, but not at the level of resolution required to perceive any difference whatsoever attributable to cables.  These guys are leading you down a primrose path that will only lead to disappointment.  You would be far, FAR better off with a little Schiit Loki equalizer to tailor the sound.  
QED silver anniversary xt speaker cables are excellent and should help. I use the bi-wire version.
Get them here...
Replacing the cables that are still the nasty OEM ones will give you the biggest benefit. 

I would suggest you buy a single powercord, that you should put on your Musical Fidelity v-150. The audience house sound is probably what your looking for - they have a special on their Forte F3 cables which is a very good entry level cable and a significant upgrade over stock. Another cable I would recommend that is not all that expensive (< $150) is a Wireworld Aurora. Both well should give you a very audible improvement.

Buy what you're comfortable affording and preferable buy one (1) better quality cord than two or three lesser/cheaper models.